i know for a fact that mine is not a hardware issue. when it acts up and i can't put it in standby, i can still mute music, calls, etc with no additional force. after a battery pull, it usually works... again, no extra force, just a normal push. if it was hardware, i should not be able to use the mute button for any function. i have the most recent AT&T s/w 18.104.22.1684 and platform 22.214.171.124, which was updated last week. i had the problem before and after the update.
i notice it most often after driving home and using the media player plugged into my car stereo. after unhooking everything, i try to put my phone on standby, and... nothing. i've turned the player back on and muted the music with no problem, placed a call and muted it with no problem, but it just won't activate standby mode. after a battery pull, it almost always will go into standby as usual. this is getting to be nearly every night that it happens, and is awful frustrating. it happened on my last bold too, same symptoms, same (sort of) resolution.
also posted on crackberry for the keen-eyed... reeeally would like a resolution