This game has a good interface and decent piece handling, however the latter introduces a serious flaw: If you stack pieces then select the full stack to move it around, the pieces end up perfectly sorted. Basically, it solves the puzzle for you. My guess is, you simply omitted to change the Z-order when or after spreading out the pieces. And indeed any latest selected piece doesn't seem to be displayed on top of its stack. (You should change the z-order when picking pieces to unsort them economically.)...