With a ports tree updated to r307547 and pkgng in use I cd to databases/postgresql92-server and run:
make PREFIX=/jails/instances/postgresql install

The usual build output and then:

===> Installing rc.d startup script(s)
===> Correct pkg-plist sequence to create group(s) and user(s)
===>   Registering installation for postgresql-server-9.2.1
pkg: lstat(/jails/instances/postgresql/include/postgresql/server/plpgsql.h): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/ascii_and_mic.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/cyrillic_and_mic.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/dict_snowball.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/euc2004_sjis2004.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/euc_cn_and_mic.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/euc_jp_and_sjis.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/euc_kr_and_mic.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/euc_tw_and_big5.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/latin2_and_win1250.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/latin_and_mic.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/libpqwalreceiver.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/plpgsql.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_ascii.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_big5.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_cyrillic.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_euc_cn.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_euc_jp.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_euc_kr.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_euc_tw.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_euc2004.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_gb18030.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_gbk.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_iso8859.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_iso8859_1.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_johab.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_sjis.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_sjis2004.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_uhc.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/utf8_and_win.so): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/conversion_create.sql): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/information_schema.sql): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/pg_hba.conf.sample): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/pg_ident.conf.sample): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/postgres.bki): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/postgres.description): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/postgresql.conf.sample): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/recovery.conf.sample): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/sql_features.txt): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/system_views.sql): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/extension/plpgsql--1.0.sql): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/extension/plpgsql--unpackaged--1.0.sql): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/extension/plpgsql.control): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/extension/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/postgres.shdescription): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/snowball_create.sql): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Africa/Abidjan): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Africa/Accra): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Africa/Addis_Ababa): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Africa/Algiers): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Africa/Asmara): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Africa/Asmera): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Africa/Bamako): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Africa/Bangui): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Africa/Banjul): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Africa/Bissau): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Africa/Blantyre): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Africa/Brazzaville): No such file or directory

<snip>

pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Pacific/Port_Moresby): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Pacific/Rarotonga): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Pacific/Saipan): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Pacific/Samoa): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Pacific/Tahiti): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Pacific/Tarawa): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Pacific/Tongatapu): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Pacific/Truk): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Pacific/Wake): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Pacific/Wallis): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Pacific/Yap): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Poland): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Portugal): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/ROC): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/ROK): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Singapore): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Turkey): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/UCT): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/Alaska): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/Aleutian): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/Arizona): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/Central): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/East-Indiana): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/Eastern): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/Hawaii): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/Indiana-Starke): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/Michigan): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/Mountain): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/Pacific): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/Pacific-New): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/Samoa): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/UTC): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Universal): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/W-SU): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/WET): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Zulu): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/posixrules): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/Africa.txt): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/America.txt): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/Antarctica.txt): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/Asia.txt): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/Atlantic.txt): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/Australia): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/Australia.txt): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/Default): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/Etc.txt): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/Europe.txt): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/India): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/Indian.txt): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/Pacific.txt): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Africa/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/America/Argentina/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/America/Indiana/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/America/Kentucky/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/America/North_Dakota/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/America/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Antarctica/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Arctic/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Asia/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Atlantic/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Australia/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Brazil/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Canada/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Chile/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Etc/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Europe/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Indian/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Mexico/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Mideast/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/Pacific/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/US/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezone/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/timezonesets/): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/danish.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/dutch.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/english.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/finnish.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/french.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/german.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/hungarian.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/italian.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/norwegian.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/portuguese.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/russian.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/spanish.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/swedish.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/turkish.stop): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/hunspell_sample.affix): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/ispell_sample.affix): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/ispell_sample.dict): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/synonym_sample.syn): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/thesaurus_sample.ths): No such file or directory
pkg: lstat(/jails/instances/postgresql/share/postgresql/tsearch_data/): No such file or directory
pkg: lstat(/jails/instances/postgresql/lib/postgresql/): No such file or directory
Installing postgresql-server-9.2.1... done
===> SECURITY REPORT: 
      This port has installed the following files which may act as network

I didn't see these problems when PREFIX wasn't specified. Looking in $DESTDIR I see the second postgresql directory is missing. e.g. the PLIST specifies /jails/instances/postgresql/share/postgresql/tsearch_data/danish.stop but what I actually have is /jails/instances/postgresql/share/tsearch_data/danish.stop

How-To-Repeat: cd databases/postgresql92-server
make PREFIX=/jails/instances/postgresql install