There are two make up slips I noticed in the film. The first is when Harry and Ron are speaking on the train. Ron has a long smudge down the right side of his nose. When they are eating sweets shortly thereafter, the smudge has shrunk to thumb-print size.

The other slip up is in the final scenes, during the giant chess match. Harry has some gashes on the right side of his face, which are bleeding, then not, then they are....... all through the fighting scenes to follow.