So it does not seem the same bug as @SaltyMedic .
There is an infinite recursive loop starting in miPointerUpdateSprite function at ../xorg-server/mi/mipointer.c:431, this relates to your usage of vnc it seems.
With this nice backtrace you can report the bug to X11 developers.
I don’t think this has any to do with KDE software.
As a workaround you could try to use RDP with krpd for instance.