Other mistake: The one demon that knew about the 40s party was vanquished, and he went straight from spying on Paige and Phoebe at P3 to "glamouring" into Leo at the Manor. He had no way of telling Devlin about the 40s party, and yet it was still full of demons waiting to kill the Charmed Ones, with Devlin "glamoured" into Melody as a trap. And Devlin didn't even have that power - the demon that was vanquished did.
Other mistake: After Piper freezes the first crime scene that Cole and Phoebe (aka Frankie and Lulu) have hit, Piper unfreezes Darryl by touching him but at the beginning of the the episode when Piper and Cole are touching the car that Piper froze, to stop it from exploding after a car crash, while trying to help the woman inside, the car never unfreezes. This is somewhat inconsistent through the entire show a lot of times they can unfreeze things by touching them and then a lot of times they can only unfreeze things by Piper using her pointer finger to either unfreeze a head or a foot or some other body part.
Other mistake: In this episode, the Source talks about the "Ultimate Power" being the Hollow. But in Season 8, we learn that the "Ultimate Power" is Billy and Christy. (And they end up taking in the Hollow, so now are they the "Ultime Power" times 2?) Which is it? It can't be both.