Comment 17 for bug 1408263

This has also been happening to me a little too frequently. It's particularly bad, given that you can't use the system without these edge gestures, being unable to return to the home screen, switch app, launch new apps etc.

Like others, this seems to happen when in a pocket, and most times when playing music. If music-app still has some kind of exception for suspending the phone, then that might explain why it happens more frequently there, if it is somehow linked to suspending.