is your alarm ringtone a big file? when i was using quite large and long mp3 (>5mb) i had similar problems sometimes, using smaller sound files made it less annoying. Still, sometimes i also have issues, but mainly related to wild uncontrolled screen rotations when phone is laying flat - when alarm goes on, the screen turns on and the alarm popup gets displayed in landscape, then in protrait and in landscape again - which makes it unable to disable the alarm in less than few seconds - maybe you have similar problem?