I am not able to reproduce it everytime, but when i'm trying the plugins of the goodies with the 4.2 beta 2, it crashes the xfce4-panel. I use a Debian Sid, with the debian packages provided by os-cillation. More information about the error and ~/.xsession-error logs is in http://www.os-cillation.de/cgi-bin/yabb/YaBB.cgi?board=deb-help;action=display;num=1099279867 Although the first time also crashed the taskbar and, posibly, the icon-box, it never happened again with these two components.
I noticed that panel crash using taskbar plugin and shelpheed claws. When this program shows a new warning window (when can't connect to pop server) and I press OK, the panel crash and not restart automatically. The panel not crash in another ways, for the moment. Regards.
There were some fixes to the taskbar, so I'm hoping this will be fixed in the next pre-release (RC1).
I'm setting this to FIXED for now, please reopen if RC1 still has the same problem.