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.
Continuity mistake: In the scene where they are having the finals, the things on the desk change a few times.
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.
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: 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.
Free Tippy - S2-E5
Continuity mistake: When Carey hands Cody and Zack the pet rocks, her handbag goes from her shoulder to her arm, back up to her shoulder between shots.
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.
Continuity mistake: When Zack trips on the slick floor, his red backpack ends up behind Cody, but in shots facing the kitchen the backpack is across the room, near the kitchen cart.
French 101 - S2-E2
Continuity mistake: In their attempt to make Esteban feel better, when London stands at the doorway shouting at Maddie outside, the colorful shopping bags on London's arm change their order in the close-up.
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.