Version:            (using KDE Devel)
Installed from:    Compiled sources
Compiler:          debian unstable up2dated gcc/g++ 
OS:          Linux

Kwin crashes sometimes badly,
I can reproduuce it with kimdaba.
Just open kimdaba, choose "Create own database" and than it crashes.
It crashes on other apps as well.

in console i got :
ASSERT: "block_stacking_updates == 0" in layers.cpp (528)
ASSERT: "block_stacking_updates == 0" in layers.cpp (528)
ASSERT: "block_stacking_updates == 0" in layers.cpp (528)
ASSERT: "block_stacking_updates == 0" in layers.cpp (528)
ASSERT: "block_stacking_updates == 0" in layers.cpp (528)
ASSERT: "block_stacking_updates == 0" in layers.cpp (528)
ASSERT: "block_stacking_updates == 0" in layers.cpp (528)
ASSERT: "block_stacking_updates == 0" in layers.cpp (528)
ASSERT: "block_stacking_updates == 0" in layers.cpp (528)

and than it dies.
I do get this error message, just once sometimes, but kwin continues to work.