Hey, following the bug report on Debian BTS (http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=547160) I noticed that it wasn't possible to change the restart style (in the "Session" tab of xfce4-session-settings). Selecting an item and trying to change it does nothing. Monitoring xfconf chanel shows that nothing is modified either. Using LC_MESSAGES=C or LC_MESSAGES=en_US, it does work. If you need more help, please ask.
Fixed in 9716629.