I don't recall this being raised on the ng before. (If it has, "Well, excu-u-u-u-use me . . . .")
A book was out a few years ago, pointing out things that weren't supposed to have happened/appeared in various movies e.g. Yul Brynner's earring disappearing and reappearing in The King & I (during the "Puzzlement" number); a Roman soldier with a tanline produced by the actor's wristwatch, etc.
I spotted a "flub" in the episode with Ram�n, the pool guy who wanted to be Jerry's friend. (Perhaps the name of the episode is "The Pool Guy.") When Newman and Jerry are kneeling over Ram�n on the pool deck (Newman having knocked the guy unconscious when he jumped in the pool), Newman's wearing a "flip-flop" on his left foot, then a cutaway happens, then back to the scene where we can see Newman's left foot again but now the flip-flop's gone. A continuity flub, I reckon.
Any other Seinfeld film-flubs? (Does the NewsGuy have a list?)