Corrected entry: In the scene when the Grand High Witch first steps on the stage in the convention room, her dress is shown as tight-fitted and far above her knee. After she reveals her true face, her dress is shown as loose and far below her knee. When she puts her mask back on, her dress is again fitted and above her knee.
Corrected entry: If the witch's secretary could change Luke back into a human, how come the Grand High Witch, the most powerful witch, had no such power to transform herself or the other witches back into their original forms as they were turning into mice? In fact, they never explain why the secretary had such miraculous powers.
Correction: This is a question, not a submission. Perhaps since the High Witch was transformed, her powers disappear. They don't need to explain why the secretary had powers.
Corrected entry: How could the Grand High Witch's secretary know where Luke and his grandmother lived?
Correction: Luke's grandmother has already said that witches stalk small children, so the witch could have easily followed him home with out being noticed.
Corrected entry: As Miss Irvine sits alone in her room, drinking tea and eating cake, she says "Didn't want to be one of them anyway," but her mouth doesn't move at all.
Correction: She isn't saying it out loud; she's saying it in her head to herself.
Corrected entry: When Luke asks his grandmother if she had ever seen the Grand High Witch, she replies that nobody ever has. Later, in the film, at the hotel Helga sees the Grand High Witch and says there's something familiar about her. Plus, when the witches are turning into mice, Helga points to the Grand High Witch. Since Helga never saw her before, there's no way she should know exactly which of the witches was really the Grand High Witch.
Correction: Luke knew she was the Grand High Witch and told his grandmother. It's not exactly difficult to describe someone who looks like Anjelica Huston. Plus she did see her, when she distracted the cat with her yarn.
Earlier in the movie, before Luke is turned into a mouse, him and Helga are in the dining room and when Helga sees the Grand High Witch in disguise, Helga says that she looks familiar but can't seem to place her.
Correction: This is not a mistake at all. If you observe the Grand High Witch in the scene prior to stepping on stage she is seen to be wearing a cape. It is actually a cape/skirt attached to the back of her dress. This is why it seems to be a wardrobe change between shots.