When a zombie starts to break a door and the zombie moves away or dies the door continues to break. (Visual Glitch) 

If you break the door then place any other block where the door was it will show as if it is breaking. (Including some unbreakable blocks like bedrock and command blocks) One weird effect is if you place lava where the door was breaking it turns really red.

This effect is not permanent. The blocks don't actually brake