Why compositing gets disabled in KDE4?

[Yuri]

It worked before on the same system (~3 months ago). But after some 
updates of everything (kernel/nvidia driver/kde4) it gets disabled from 
kde4 startup. Pressing 'Resume Compositing' doesn't help.

Message pops up that some application disabled compositing, press 
Alt-Shift-F12. But this doesn't help either.

Any idea why this feature is broken?

FreeBSD-8.1-STABLE amd64
nvidia-driver-195.36.15
GeForce 9400GT
kde-4.4.5

Yuri