The Story of a Divorce - S1-E14
Revealing mistake: In the scene where Reba and Parker kiss outside the restaurant, you can see creases in the scenery backdrop behind Reba.
You May Kick the Bride - S1-E15
Revealing mistake: When Reba goes to leave the church and walks on and rips Barbara Jean's train, Reba looks down before she walks on the train to ensure it will rip. This is not a cruel joke by the character, but rather a mistake by Reba McEntire due to her character's reaction immediately after.
Up a Treehouse with a Paddle - S1-E21
Revealing mistake: When Brock finds Reba holding baby Henry in the kitchen, you can see a doll's face in the blanket.
Answer: I believe it was "Seeing Red" from season 2.
Karoo