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.
The Suite Smell of Excess - S2-E15
Revealing mistake: When Arwin tries to use the P.U., when the door is closed, you can plainly see a reflection of Cole Sprouse waiting offstage.
The Suite Life Goes Hollywood (2) - S2-E37
Revealing mistake: When Maddie and London are pulled off the cart by the horse, you can tell they use dummies. Look at the way their bodies move.
Audio problem: When Cody orders the Number 8, someone says, "We got a Number 8". But no one's mouth moves.
Continuity mistake: In the scene where they are having the finals, the things on the desk change a few times.
Revealing mistake: When Arwin admits he cheated, on one of Arwin's lines, the guy behind Mom (the guy with the clipboard) silently mouths along with that line.
The Suite Life Goes Hollywood (2) - S2-E37
Revealing mistake: In the scene where London and Maddie fight and fall off the the saloon balcony, you can see that they are stunt doubles.
Other mistake: When London is reading her book to the little children, the small girl wearing pink with a ribbon in her hair is miming what London is saying, just before London actually says it.
Visible crew/equipment: In London's suite, when Arwin opens the door to the porch where the hawk is nesting, the reflection of a crewmember wearing a white shirt is visible on the door's glass panes.
The Suite Life Goes Hollywood (2) - S2-E37
Revealing mistake: In the scene where Maddie and London come out of the saloon scratching and clawing, you can see that they're played by stunt doubles; the stunt double playing Maddie doesn't have any bangs, whereas Maddie has bangs.
Revealing mistake: After Arwin scores the winning spare, Esteban and Mr Moseby lift him onto their shoulders. When they drop him there is obviously a large pad to catch him as you can see his legs stick up in the air between Maddie and Esteban. It is even more noticeable as he bounces up and down on the pad a bit.
Revealing mistake: At the end of the episode, when Moseby and the rest do the dance number, London falls from the stairs onto the floor at the bottom, near the candy counter, when she hits it, you can see the corner of the blue crash mat come up.
Revealing mistake: The whole time London is on Maddie's back and is dropped off, the stunt doubles' faces are noticeable.
Odd Couples - S2-E1
Audio problem: The delivery man's (pushing the plasma television) lips are not moving at the top of the video.
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.
Visible crew/equipment: When Cody and Zack walk into London's suite and find Moseby there, crewmembers are reflected on the glass door behind Cody. First in the wideshot, when Moseby explains the plan to capture the bird and then in Cody's close-up.
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.
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.