I spotted this slip-up while watching the movie with a friend. It takes place when the T-Rex parents begin to push the trailer over the cliff. Right after Malcolm says "Hang on, this is gonna be bad", the window in the very back of the trailer falls off to the side. This window also only extends to just below the bars on the back door.

When the trailer is halfway over the cliff the door falls off and Sara falls down onto the glass window that had previously fallen off. It has also extended the whole length of the door!