Continuity mistake: When young Al reaches forward with his left arm to take the book that Miss Degroot wants to give to him, she quickly pulls back but young AL still has his arm raised. In the next shot, his hand his down by his side.
Revealing mistake: At the start of the episode, Peg is making popcorn on the stove. It's making a sizzling sound like she's really popping it but the burner isn't even on.
Revealing mistake: Peg is making popcorn on the stove. It pops even though the burner isn't even on.
Answer: It's implied that Steve filed for divorce since in s04e16, "You Gotta Know When to Hold 'Em", Marcy says that Steve is suing for alimony. Alimony is something that has to be requested when filing for divorce. Although the show doesn't spend time on the actual legal proceedings of their divorce.
Bishop73