Siren Song - S5-E4
Other mistake: When the siren gets the pole that was speared through her pulled out, there is only blood in the middle part of the pole. If it had really been pulled out of her, it would be bloody all the way along. (00:19:55)
Siren Song - S5-E4
Revealing mistake: When the Siren is being healed, you can see that she's just holding the pole next to her, when it's supposed to be going straight through her. (00:19:50)
Siren Song - S5-E4
Character mistake: When discussing how best to help Melissa, Piper tells Paige that her birth father was half whitelighter, when he was fully a whitelighter. (00:25:15)
Siren Song - S5-E4
Continuity mistake: When Piper and Paige fall out the window and land in the dumpster, in the wide shot the garbage bags are white, and in the close-up they're blue. (00:16:45)
Siren Song - S5-E4
Visible crew/equipment: While Leo is at the manor with Phoebe, who volunteered to make the potion, when Piper and Paige orb into what's left of Melissa's home, through the hole in the wall we can see the boom mic (with a white striped tip) hovering over the sisters, just as Piper tells Paige she doesn't want to make Melissa more upset. (00:24:45)
Siren Song - S5-E4
Visible crew/equipment: While Piper and Paige are talking in the kitchen they hear the news report about the fire, and when it cuts to Leo watching the news on TV we can see the red T-mark taped to the rug's red design. (00:06:35)
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.