I think there was something very wrong with the power kernel released around 10 or 11-11, I got also problems with camera (all cam applications) and got screen-glitches in menus ... (sometimes so bad I could not see the menu)
Today I had a new update for power kernel and this fixed everything (you just need to be aware that also U-boot is implemented now in the power-kernel so you will see a U-boot when restarting your N900 after the update)