Some of the TTT users at my company have reported the same issue and I've seen it once myself.
If you change the time or date on your system backwards in time a few minutes, TTT will not "tick" the minutes until the clock catches back up to where it was before it was changed.
For example, it's currently 2:06pm. If I change the time back to 2:00pm, my timecard will not be...
2009-08-18 20:37:33 UTC in Tiny Time Tracker