Wrestling with Demons - S3-E12
Deliberate mistake: When Piper froze the demons (near the wrestling) one of the demons moved when she froze him.
Extreme Makeover: World Edition - S7-E12
Deliberate mistake: While Beta, Leo, and the sisters are walking through the sleeping city Paige notices someone in a "bad suit" moving, and as she walks over we can see a bit of the white writing on the SUV's spare tire cover, at the left side of the screen, but when Paige declares she's not paranoid that white writing has been edited out in this shot. (00:26:00)
Deliberate mistake: When Zankou and the Charmed Ones force the Avatars to "put the world back" by rewinding time, in the first shot of people waking up note the Jeep in the backround. The problem is the words "Jeep Liberty" are on the spare tire cover in this shot, but in the previous episode "Extreme Makeover World Edition" that spare tire cover is all black because those words were edited out in two shots. The first shot is when that group of people fall asleep, and second shot is when they all wake up the first time. (00:35:15)
Answer: That was a mistake in the series.
Also, the episode is called 'Babies First Demon' and this alone tells us that it's Wyatt's first time in the field (so to speak) and as the sisters say, they've done a good job of clearing up their own magical messes so far. Nobody really knows how advanced Wyatt's powers are, or will become. That's why the cleaners appear, to nip things in the bud. The Cleaners didn't want to chance that the sisters could clean Wyatt's magic up, just incase they couldn't. Therefore intervening themselves, just in case.