It's one of the most renowned errors in movie history. When entering the docking bay command centre on the Death Star, one Stormtrooper clumsily bangs his head on the opening door. George Lucas is clearly aware of the mistake; not only did he add an audible clunk into the special editions, but he attempted to provide some context to it in the prequels.
When leaving Kamino following his fight with Obi-Wan, Jango Fett, the genetic model for the clones, bangs his head on the door of Slave I. It's a nice joke, but does raise a heap of problems. Suddenly hitting heads on doors is a genetic trait, while it's hard to believe the Empire would be using twenty year old clones on its flagship space station.