Well at least we know how they're doing it. I don't know what's the fun in cheating. With their other games (suduko, etc) they have it set so you can only do the puzzle one time. If you click out of it to start over on the other puzzles (which I did yesterdayon the jigsaw puzzle because just after I started, I got 3 phone calls), it tells you that you've already done the puzzle for the day and doesn't allow you to do it again.
I think that is a great idea, but I wish they would allow pause (by blackening the screen so you can't see the pieces) on those games for those times when you do get a phone call etc. (I honestly believe I would have gotten 3rd or 4th place on the jigsaw if I didn't get the chance to start over, since the pieces became somewhat familiar to me.)
I tried clicking like you said to do Doris, but it didn't work for me. Hopefully Derek fixed it?