Like level 26 "in series" for example. I will have pushed one of the hearts into the heart block, then joined the line of items in between the two 1s and pushed up into the portal. When I come out the bottom, everything resets.
Ah yes, that's an infinite series of rooms -- entering the portal does not "reset" the room, it brings you to a new room with the same layout.
OHHHH... that makes a lot more sense. Thanks. I love this game, even though it makes me feel stupid. It's probably the most challenging and most rewarding game I've ever played. Still desperate for a walkthrough or some hints, though.