De-Kahnstructing Henry - S3-E13
Deliberate mistake: In the scene where Hank is mowing his and Minh's (Khan's wife) lawn he mows straight across from Minh's lawn to his own lawn. This would be impossible as in every episode including this episode (before and after this scene) there is a fence separating his house and Khan's house. It was likely removed to simplify Hank's going back and forth between the two ladies as they try to gain his affection with food and beer. (00:15:30 - 00:16:40)
The Wedding of Bobby Hill - S3-E14
Deliberate mistake: As Luanne is putting the dirt into Bobby's fruit pie you can see she rips open a large part of the packet. Yet in the next scene when Bobby is about to eat the pie there is no sign of where Luanne ripped the packet. Its likely this was deliberate as the joke in the scene was Bobby and Luanne's constant attempts to get back at each other, if they had left the large hole its likely Bobby would have not fallen for Luanne's prank.
Answer: Couple things, first only Peggy knew the truth about Hoyt (Luanne's father) being in prison and Peggy is the one who said he's on an oil rig. But, Hoyt is Peggy's brother, so she could have been trying to hide the fact her brother is in jail. Lucky (Luanne's husband) deduced Hoyt had been in prison, but seems to be the only other person to know the truth, so when Hoyt went back to prison, he kept Peggy's lie up to spare Luanne. Additionally, Luanne was there when her mother stabbed Hoyt and was arrested, so it's not like someone had to break the news to her and they couldn't hide the fact. With Hoyt, even if Peggy wasn't trying to protect her brother's reputation, she didn't want Luanne, who is a sensitive and emotional young woman, to have to deal with knowing both parents are in jail.
Bishop73