A couple people have come across a bug when running on iPhone3.0. Occasionally the "X" button on the puzzle playing screen can stop working. I've just submitted a fix for this to the app store (version 1.6).
If you come across this problem then there are a couple of workarounds, you can use the undo button to remove the number you just entered, or you can just overwrite the wrong number with the correct answer.
Posts
