Glitches often, for example it regularly won't allow you to pay for a city upgrade on your turn when you have enough commodities to do so. I think it happens more when you've traded for a commodity, the software won't register or recognize that you now own that commodity. And when playing against other players and someone is meant to be first to place their settlement people will often run the clock timer out so that they don't have to pick first. Games are only fun if they're fair.