Ehi, first run i couldn't undestand but i did at the second time. When you press the "last button pressed" again, that button, that usually represents the "down" button, becames the high button... shouldn't be better to give some feedback to the player on what the "last button pressed" represents?
(even the key shown on the high/low side of the square. not a great visual feedback sure, but at least it's visible ).
(The rest is good, this was the weird element, but it's probably given from the out of control theme)