There was an issue where if there was a block above a dropping block and you pressed the space bar, then the dropping block would move on top of the block that was above it.
At first I thought the issue was that the input was going too fast, so I tried to make a delay after pressing the space bar, but that was not the issue.
It turns out there was a bug in the function being called by the space bar. It tried looking for the max y to place the block, but the y range should have been smaller. The range should have been from 0 to the block's y rather than the max available on the grid.