I've just had a report from a Debian user using “zaphod mode” (where two X servers are running, afaict) and having issues with xfce4-terminal “server” mode.
Basically it seems that when a xfce4-terminal process is run on the first X server, trying to run xfce4-terminal on the second screen makes the initial xfce4-terminal process crash.
It's apparently a regression from 4.8.
Downstream bug is available at http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=710002 and original reporter should be reachable by mail if needed.
*** This bug has been marked as a duplicate of bug 10124 ***