I get a frequent bug where certain blocks/squares can't be dug. The dupes just keep zapping the block, the task bar fills up, but nothing happens. I have to cancel the dig. If I then save and resume the game, the dig task completes itself automatically. I get these frequently (probably one every twenty/thirty blocks I dig) so I have to restart a lot.
Assign dupes to dig a large number of blocks. A few blocks will be undiggable, without fail in the dozen or so games I've started and abandoned.