i get the following fascinating bug: Lets say i place a wooden floor, did it wrong and want to remove it immediately (cursor still on the wooden floor icon), i place a second floor tile over the first, instead of removing the previous. If i then select another item i can remove the second one but the first is permanent. After a reload the first tile is gone.
This bug works in combination with asphalt too. Means, i can place a wooden floor over asphalt, and when removed the asphalt is unaccessable at first and gone after feload.