Other mistake: The characters that are supposed to be native to Boston, Massachusetts, i.e. Maddie, Maddie's parents and Red Sox fans, don't ever actually speak with the iconic Boston accent.
It's a Mad, Mad, Mad Hotel - S1-E12
Other mistake: In the episode "Its a Mad, Mad, Mad Hotel", when Esteban has his dream of becoming rich and London becoming his "Bell Girl", he calls the hotel "Hotel Esteban, but London's uniform still has a "T." When it cuts there is an "E" on the front desk.
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.
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.