Visible crew/equipment: When the Conners' friends come over and say "Hey Jailbird!" to Dan, a microphone can be seen coming down and going back up in the top left corner.
Revealing mistake: When Dan calls Becky, there is a shot of her and Mark in their Minneapolis apartment. This is the exact same set that is used later for Darlene's Chicago apartment when she goes to college. The fireplace shape and style, the wallpaper, position of the bathroom door, and the windows are exactly the same. The only difference is that the Darlene version looks shabbier.
Revealing mistake: After Charlotte picks out a dress with Roseanne in the kitchen, and she tells Darlene that she should also go to the prom, she runs from the kitchen like she is going home, but she is running between the kitchen and outside wall of laundry room. (00:08:00)
Visible crew/equipment: While Darlene is at the jail to post bail for Dan, when she says, "I guess I should prepare you for all the things that have changed," the boom mic casts a shadow on the wall, at the right side of the screen. (00:04:25)
Other mistake: After the crazy guy threatened Roseanne when she was working alone at the Lunch Box, Dan wanted to teach her and Jackie how to use a gun for protection. Dan seems to have forgotten that Jackie was a cop for the Lanford Police Force and already is trained in firearms use. He regularly saw her in uniform with a sidearm.
Halloween IV - S5-E7
Plot hole: Just before Roseanne arrives at the Lodge Halloween party, Fischer is holding a small object in his hand that he slightly adjusts to a certain position. Roseanne then arrives dressed as Lady Liberty. When she raises her torch and asks someone for a light, Fischer immediately flicks on the cigarette lighter that he was already conveniently holding and ready to ignite for no apparent reason.
Answer: Clearly, the only person who could truly answer this question would be a set designer for the series, or someone else directly connected to the series who would have this kind of detailed information. I looked on IMDb.com and Cheryl Lanner is credited as set designer through 1997. I quickly found her Facebook page, and I directed your question to her. After some time, Ms. Lanner has replied as follows: "I decorated the last season 1/2 but after 9 seasons the sofa just plain got worn out and had to be repaired from 8 years of usage. There was a board put on the sofa but as I've said, it was due to so much usage. If they had back problems I was unaware of them, but you can be assured that if that was the problem it would have been fixed immediately. Take care Michael!"
Michael Albert