Continuity mistake: When one of the older twins in the wheelchair throws the apple and his twin catches it, we see that nobody is standing on the stairs in front of the main entrance. Though in the previous and following shots Moseby is actually standing on the second step.
Neither a Borrower Nor a Speller Bee - S2-E12
Continuity mistake: When Maddie is painting the apartment, London is reading the article about Porsche's charity work, and the actual newspaper changes between shots.
Continuity mistake: Right at the start, when Zack is hanging on the tree branch, the long sneaker laces are in front of Cody's shoulder, but when Zack falls, they're gone, though the sneakers have not moved.
Volley Dad - S2-E24
Continuity mistake: Towards the end (during the closing credits) when London comes and find Maddie sleeping on the bench, they talk for a while and you can see Maddie has her bag beside her but when they leave the bag is still on the bench.
The Suite Life Goes Hollywood (1) - S2-E36
Continuity mistake: After eavesdropping on Bud and Lou, when the 'hitmen' open the door, the things on the tray Bud is holding keep moving around between shots.
First Day of High School - S3-E10
Continuity mistake: In Season 3, "First Day of High School," when the principle is telling London that she cannot build her lounge, the position of her hands change from being on her hips to being in the air.
Answer: Keep in mind, Muriel wasn't very popular. So the writers/directors must have thought it'd be a good idea to let go of the character. No one seems to be complaining.