iPhone Clock / Timer app problem - can't set timer for over 1 hour.

If I set the timer for anything over one hour, the digits display incorrectly, e.g. 1 hour 1 minute displays as 'h:1:01 a' and the timer doesn't count down.

I have an iPhone 5 running 1OS 6.0.2, although I was experiencing this problem with my previous iPhone 4S, so the problem seems to have carried over.

Does anyone have any idea how I can fix this?