Currently building portdowngrade package on a clean system will only install subversion 1.8 even if 1.7 is defined in make.conf with WITH_SUBVERSION_VER=17.
Linked patch by Olli Hauer fixes this and will install either 1.7 or 1.8 as required for the run dependency.
A commit references this bug:
Date: Wed Jun 11 21:00:24 UTC 2014
New revision: 357538
Submitted by: ohauer
Submitted by: Simon Wright