Santa's Little Helpers - S6-E11
Continuity mistake: When Shawn and Angela are talking in the student union building, Shawn's scarf is draped around his neck in an asymmetrical fashion, with the left side shorter than the right. When they sit down on the couch, he pulls the two sides to a symmetrical length. Throughout the rest of the time Shawn remains seated on the couch, the two sides alternate between being symmetrical and asymmetrical. (00:15:20 - 00:16:47)
Answer: Topanga's middle name is never specified. Considering her sister's name is Nebula Stop-the-war Lawrence, Topanga's is probably something equally unusual.