I made exactly the same observation in a dual seat configuration with KDE4 on the second seat only. With 285.x everything was OK, with 290.x and 295.x the bug was observed.
Very annoying, leaves the whole configuration unusable. Restarting X helps, until the next logout.
Already sent an nvidia-bug-report.log.gz to email@example.com
, but they answered, that they do not support dual seat configurations.
SLES11SP1 / Two Quadro FX3800 graphics cards.