@Schoening - I think it has to do with this:
Essentially, newly created instances cannot be picked until the next top-level event. You could put your sorting loops in a function, and beneath the action "Move to bottom of layer", add "Wait (0)" and then a call to the function - that would probably fix it. Can't test it right now, unfortunately...
edit/ If you're trying to adjust z-order, could you not just build the tiles from the top down? That should create them in the proper order. Or maybe I'm completely misunderstanding...rogueNoodle2013-04-12 12:08:23