Alarms don't stop if not stopped soon enough
If an alarm is permitted to run for long enough, it doesn't stop, and runs multiple alarm ounds at once. (the 5 minute alarm if left never stops ringing, and the one minute one sometimes exhibits this issue)
What appears to be happening in the code is bell.ring() is getting called multiple times if the alarm is permitted to ring for long enough. This causes the alarm to start running multiple sounds at once(sounding pretty awefull), and it seems stopping the alarm bell after that point only stops one bell from ringing when bell.ring() has been called multiple times, thus making an alarm that doesn't stop.
This is a very common case for users, as one may be too occupied to stop the alarm (ie driving), or have left their phone somewhere, and thus can't stop the alarm before it becomes unstopable. It's been mentioned a lot in the forums.