This problem seems to be very intricate with many "if"s, so I try to explain it as I digged into it:

The problem: When net-im/centerim is compiled on a system without devel/ncurses, everything is good. However, when devel/ncurses is preinstalled and net-im/centerim then compiled, terminal output is broken.

The reason: It includes system ncurses.h, but uses ports libraries.

The explanation: System ncurses.h and system libraries libncurses/libtinfo define and use chtype as 8-byte long, but ports ncurses.h and ports libraries libncurses/libtinfo define and use chtype as 4-byte unsigned. The worst case is in definition of library's chtype acs_map[], which is used in application through ACS characters as ACS_* macros. If the headers and libraries are mismatched, the application do not reference correct ACS characters. Sometimes it writes nul characters (@), sometimes it dumps core.

When port has USES=ncurses and devel/ncurses is installed, the port should use -I${NCURSESINC} in CFLAGS and -L${NCURSESLIB} in LDFLAGS. However, it is not sufficient itself.

But why sysutils/screen with just NCURSESINC/NCURSESLIB does work? It is because it does not include any of ncurses headers. It needs just tget*() function family, and it is defined itself in osdef.h, without any external header. If you try to include ncurses.h in screen.c, you end on 'ncurses/ncurses_dll.h' file not found.

Well. And why net-mgmt/cnagios "works" without NCURSESINC/NCURSESLIB, linked with ports ncurses and included with system ncurses.h? Because it does not use ACS_* macros.

And so on. It seems to me that every port using ncurses is another case for itself, where universal instruction would be:
Add "-I${NCURSESINC} -I/usr/local/include" to CFLAGS and add "-L${NCURSESLIB}" to LDFLAGS, but as I feel, it does not look systemically at all.

I think that fixes are needed by both: Ncurses infrastructure and ports using USES=ncurses themselves. Sometimes they do not work at all, sometimes they just look that they work, and sometimes they would be correct.