The Case of the Fickle Filly - S6-E11
Other mistake: George Tabor parts his hair on his right side, however when Perry cross examines Mr. Tabor his hair is parted on his left and then reverts back to his right side. The two dots on his tie are one low and one high, they also switch. The negative must have been flipped.
The Case of the Capricious Corpse - S6-E2
Revealing mistake: The murder victim is seen through the legs of a chair - just as the scene changes he blinks. (00:11:00)