Revealing mistake: In the episode "Out on a Limb", Jack leaves Terri in Mr. Townsend's office lobby to keep the secretary busy while Jack is supposed to climb a tree outside up to the window and move from window-to-window to get to Townsend's office. If you look at the window behind Terri and the secretary, you'll see Jack magically walk through the brick wall to get set up for the tree climbing scene.
Visible crew/equipment: After Jack talks to Larry about the magazine quiz Jack asks Janet if anything's been bothering her, and just as Terri walks out of the kitchen holding the two cans, a crew member's hand can be seen behind Terri placing a bag on the counter.
Visible crew/equipment: Near the start of the show, money comes out of the ATM by error. You can see the money waiting in the slot and the crewmember's hand pushing the money out sporadically. It also comes out sideways sometimes, sometimes not and out of different parts of the slot.
Add timeterry s
Other mistake: Larry entered Jack as "Grandma Tripper" to win the contest since the contest was only open to women. However, since Larry admits he didn't know there would be a bake-off and thought a winning check would just be mailed, then there's no reason to of entered Jack as "Grandma." He easily could have just entered Janet or Terri using Jack's recipe.