My goal with the level was to come up with something entirely new. I figured all of you have tried every combination of elements by now, so I went into the code to look for ideas for the level. Then I came up with this bit. The main game engine sets up a level (once per frame) in rows from left to right, and rows from top to bottom of a level. It figures out what to do with all the elements, then updates the game for the next frame. So a box that was created to the left or above another box is 'created' first and then has a tiny bit of priority. E.G. it's movement is completed a nanosecond before the next box, etc.
Leaving the boxes in their current order, the left box will move first, and hence bump into the last bit of the other moving box at the conveyorbelt corner - boom. Switch them, and now the box that is now in 'first' on the belt will move around the last bit of the corner first, before the second box catches up. And so they miss each other completely.
No way you could figure this out without knowing the innards of the game engine. Hence the title of the level.
Actually, the first title of the level was 'Now that's just mean!', which was fitting, too.Feel free to play with this idea, or not. If you do want to try this on your own, I'd would definitely suggest that you post a sign in the level with a clear indication that you're using a trick along these lines - both to warn people and since (obviously) this type of trickery is few people's cup of tea.
There you go - Wonderland Physics explained. Class dismissed.