Other mistake: Squirrels are used in the factory to get nuts out of shells. Mr Wonka states that they tap the nut first to make sure it isn't a bad nut. However, this is never done until the action is pointed out.
Continuity mistake: The jacket that Violet wears has a zip. However, this zip disappears without trace once she is a blueberry, and remains missing for the rest of her existance as a blueberry. Violet's body was done in CG animation, so it could not be that Violet had to change into a different costume. There was no reason why the zip couldn't remain, it just seems like the CG makers got tired of it being there.
Continuity mistake: When Dr. Wilbur Wonka is checking Willy's teeth using the dental pick and mirror, the view from inside Willy's mouth shows Dr. Wonka holding the mirror differently in his left hand from the shots of his left hand outside Willy's mouth.
Continuity mistake: After Augustus shows his golden ticket he eats a second bar. His father is behind him, holding sausages at chest level. A shot later his arms are at waist level, without him having had time to lower them.
Continuity mistake: In the beginning, where it is showing how the Wonka chocolate bars are made, we see trays holding twelve pieces of chocolate. When it shows the trays on the conveyor belt, each tray holds fourteen pieces of chocolate.
Answer: Wonka is simply uncomfortable around people. Gum chewing is simply an annoyance he never had to put up with as a recluse.
JC Fernandez