I got similar problems with my new n9. But it seems that the hint with disabling the device in console won't work!

Can the seetings be wrong, because sometimes it seems that the stupid sensor works. But most of the time as soon as I start a phonecall the display goes black! As long as the other side won't quit the call I'm unable to do anything.

Are there any ways to check the function of proximity sensor? Some sort of testing utility? Or a path in filesystem that is beeing frequently written by any driver and I can monitor?

BR Daniel