I just installed kde4 on my development system.
I can confirm this crash, but only if composite is enabled.
It's really hard to track down, because if the crash occurs, the program ends and no backtrace is available, if I run the program with --sync, I am not able to make it crash.
It's most likely a wxWidgets or xorg bug and not a C::B bug, but unless we see where it really crashes it will be nearly impossible to solve.