Other mistake: After the turkeys start attacking in "The Running of the Turkeys", Mr. Fishoder and his brother start running. In that clip a Turkey pops out the side of a guy's head. Look in the mid lower right side. Looks like a design error. Pretty big error, no slow down needed to see it. (00:05:20)
Other mistake: Anders, Blake, and Adam help promote Alice to become the boss. Before becoming boss and cleaning up, she had a very casual attitude and is shown wearing informal black, rebellious clothing. However in 3-10 "Flashback in the Day", when Anders, Blake, and Adam first meet Alice she is the same strict, formal boss seen predominantly in the show. So basically TAC in the Day makes no sense, because Alice was already boss by that point in time and already had met the gang before their first day at work. She recruited them, after all.
Other mistake: In the end of the title sequence, Jessie walks outside. Before exiting, you can see that she is just a little bit taller than the doorway, but her head passes through the frame as she walks forwards.
Other mistake: When there is an establishing shot of Outdoor man there is a California state flag on the roof. The show takes place in Colorado.
Other mistake: In the beginning when Jess is showing the guys her outfit for Cece's party, you can see she is wearing blue platform high heels. She walks in them just fine. But the next day, when she's filling in for Cece, she's given platform high heels and can't walk in them at all. (00:02:37 - 00:15:17)
Other mistake: They say that when Jack is back, they will be in college, but they were in Year 8 and all 14, so they would be, at most, in Year 12.
Other mistake: Nicole is through a window of the house in the scene when Darwin asked "Which one is the real Gumball?" This is probably from the episode "The Goons." (00:00:05)