From kde.eclass: IUSE="debug xinerama elibc_FreeBSD" [...] DEPEND="sys-devel/make dev-util/pkgconfig dev-lang/perl x11-libs/libXt x11-proto/xf86vidmodeproto x11-proto/xineramaproto" As you can see, the xineramaproto dependency is always being pulled in, no matter whether USE=xinerama is set or not. This was different in version 1.186 and older and should IMO be restored.
thanks - I reverted the change and added the xinerama use flag back due to diego's current vacation.