I've never heard of this before, and I think this would be a pretty serious issue I would hear about if it were happening to others. Are you sure the round wasn't set to a longer time than you thought? Is the clock configured to display the number of hours in a round? If not, and the round is set to, say, 1 hour 30 minutes, you would still see "30:00", and when it reached zero it would roll back to 59:59.