A Very Brief Encounter - S9-E3
Plot hole: In season 9 episode 3, "A Very Brief Encounter", Ben is upset when he learns that Susan named Nick, Janey and Michael after lovers she had in university. But in season 4 episode 6, "Deliverance", there was a flashback of Nick's birth and we learned that it was Ben who named the baby. He heard someone say the word "nickname" in the delivery room and named his son after that.