im pretty sure this is a well known issue, its been affecting mine since day 1 that i got it, on receiving a call mainly. it flips from landscape to portrait and back, sometime the answer button works sometimes not.

having thinks like microb open while the phone is dark can cause issues i find because as soon as you wake it up the web, widgets and any other web connection on that screen or in background trys to refresh

No fix best i know, i regulary run OptimizeN900 script though to keep it running smooth