Well ouch, you pointed pretty much every major flaw of the game we noticed, and we totally agree with you.
1) the bull in the wall
Yes, it's a bug, I forgot to round the position after each step, so the excess deltatime builds up when a game is too long, and it's especially noticeable on web player since the framerate is a bit lower. We noticed that a little bit after the closure of the submission, it was easily corrected, but too late :(
But the game is beatable since no puzzle is long enough for the offset to be 1/2 tile big.
2) the level 7 is super hard
Yes, the idea was to make one last level with only the basic elements of gameplay, but we underestimated it's difficulty. This was probably because we tested the puzzle with the solution in mind and not a lot of time.
3) the play button is not pointless
It prevents failed allocations and allow you to test allocations in your mind, it's useful later on too.
4) clunky UI and too long white screen
Yes, the white screen is way too long.
Our game is far from perfect but the fact you are the first one to play it enough to find all the flaws means a lot to us !
So thank you !
Edit : for level 7 put 5 tiles on button 1 and 3 on button 2 (yes the UI doesn't suggest you should put 5 tiles in one move, sorry)