OK, Go to the part when Wayne and Cassandra 's father are fighting with the swords, Wayne gets cut by one and it shows his pants and they are all ripped up and then in the very next scene they are back to normal.
That is supposed to be like that-because they are making fun of the kung-fu movies. obviously it isn't a slip up because how could the director or someone miss that? it's not a slip up. period.