Other mistake: When Prue astrals back to recite the spell to reverse the awakening spell, she and Phoebe don't actually complete the spell, they just recite the first paragraph "What was awakened for its sleep, must once again slumber deep" the rest according to the book of shadows is "return the disease to whence it came, so life can ease back to the same".
Size Matters - S4-E5
Other mistake: Since when are managers, on a trial basis no less, allowed to renovate and change the name of a club?
Suggested correction: Piper says in the episode that she allowed him creative control because the club wasn't doing well, and he was well-known to be good at what he does. It's made clear throughout the episode, by way of him telling her multiple times that if she doesn't like it that he'll get rid of it, that she still has full veto power on any changes.
Other mistake: Yenlo explains that he escaped limbo through the water in the clouds. And the yen master says there is no other water around. So why do the girls come in through a cave? If they have to leave through the water in the clouds they should enter through the clouds.
From Fear to Eternity - S1-E13
Other mistake: No one, including the cops, seem to think that all the victims' hair turned white is strange, as if getting scared to death actually turned your hair white.
The Courtship of Wyatt's Father - S6-E16
Other mistake: When the Darklighter shoots Leo in the attic on the Ghost Plane, the arrow goes all the way through him. He wasn't shown to be using anything other than a normal Darklighter Crossbow, and there wasn't any evidence that, since Leo and Piper were still alive, that the physics of the Ghost Plane are any different from the Normal Plane. Yet, in every other instance of someone getting shot with an arrow from a crossbow, it never, ever penetrates the person's body, and always get stuck.
Other mistake: When Piper and Paige are talking at the Social Services building, Paige talks about one of her coworkers, but in the closed captions, the speaker is mislabled "Piper." (00:41:30)