Well the change to libxcb fixed things for libxcb and libX11... too bad ssh didn't parse the screen out of $DISPLAY like it's supposed to... =/  I have a workaround for that in libX11 now:

http://cgit.freedesktop.org/xorg/lib/libX11/commit/?id=aae2a4a7aab26de3fa715d6ecd0a0e0926b37fc9

If we ever decide to support multiple X11 screens, we'll need to revert that (and have ssh fixed).

Here's a replacement for libX11.6.dylib with the workaround:
http://static.macosforge.org/xquartz/downloads/testing/libX11.6.dylib.bz2

(I won't be rolling an updated beta just to fix this... beta3 addressed the main issue, and the workaround is easy enough)

--Jeremy