There's a bug – BOXD - Without the E Review

If you combine two boxes, and when they're in the animation of merging, slide another box at it (It has to be the same type of box as the first two), it'll create a box an extra tier higher. For example, if you merged two space boxes, and while they were in the merge animation, dragged another space box into the spot they were merging, you would get a sky box, not a watermelon box.
Review by Vortex? on BOXD - Without the E.