When adding a system tray to the desktop via either drag and drop from the Add Widgets dialogue or by double clicking the relevant icon in that dialogue, the desktop and all panels disappear. They reappear a few seconds later. The Dr. Konqi crash dialogue does not pop up. Kubuntu 11.10, KDE 4.7.2 I do have a system tray already in a panel, I did not test what happens if the panel system tray is not present.
I am currently experiencing this problem also. I used to have a system tray in a panel, but when I upgraded from 4.7.2 to 4.7.3, plasma crashed and upon restart, my panel was gone altogether. When I created a new panel, it disappeared every time I tried to add a system tray to it, and the same thing happens if I try to add one to the desktop. Like the original report, the desktop and panel reappear after a few seconds, and there is no crash dialog. The applications menu and desktop switcher on the left side of my panel get switched every time this happens. Gentoo, KDE 4.7.3 (I did not experience this problem with KDE 4.7.2)
Created attachment 66197 [details] stack trace I managed to get a stack trace. Let me know if it would be useful to recompile libc and glib with debugging info.
Duplicate of https://bugs.kde.org/show_bug.cgi?id=282552
Marking as duplicate, thanks for the report and the backtrace! *** This bug has been marked as a duplicate of bug 282552 ***