sorry I was vague, I realized replaying it today it is actually on every level and so maybe it was intentional on your part. The brown block is possible to be pushed into the black void surrounding the floor and become irretrievable, and due to the fact that you can't restart the level and the "reverse" key doesn't seem to work all the time, it means you have to restart the entire game to get back to the point where you were. I think a fix for this would be to make it so you can restart the level, rather than rewinding your steps. If this was an intentional feature to make the game more difficult, maybe the block can disappear (or even have a simple falling animation) when pushed into the black void.