Quite a clever game! Levels 13 and 14 were the first ones that stumped somewhat stumped me. More border-based levels would be cool.
When the player attempts to push two or more blocks simultaneously, instead of pushing all of the blocks together, some weird shuffling patterns go on, and then only the furthest block in the stack gets pushed in the intended direction, the other block goes back to their original positions, and the player overlaps with the closes block.