To clarify about the clipping: most of the time, I clipped OFF of the 2x2 blocks, not through them. I'd be about to land, then suddenly my position would jump one or two units to the left and I'd fall off beside the block. It's also not just the sword power because the one time it happened on my replay, I had the fireball power. ...but I guess it's moot if the engine update fixes things on its own.
For the ice power killing frozen enemies on accident, you could do what NES Metroid did and make it weaker than your base powers, so it'd take two hits to kill an enemy that would otherwise instantly die from jumping on it once, three hits to kill an enemy that'd normally take two, etc. You could maybe also make it so that the first shot that freezes the enemy doesn't deal damage itself.
Anyway, I noticed that the second painting in Dismemberment Ward is blocked by a wall of bricks, but the only powerups in that level are the green Mega Buster and an Ice Flower, so nothing that can actually break through a wall of bricks. All of the previous levels DO have the powerups necessary to get their paintings, so again I ask: was this intentional? I had saved and quit right before this level, so I went in without a power and had to back out and replay it after pulling a sword carrot from my inventory.
Also, it'd be nice if the penguin cop let us know that the rock power isn't used by pushing the attack/run button, but instead by pushing down; that took me a minute to figure out.
EDIT: Would be nice if it was easier to figure out which paths lead to the paintings in Teleporter Maze since you can't go back once you enter a teleporter. All the other levels let you backtrack if you realize you missed a painting.