We're Off to See the Wizard - S4-E19
Continuity mistake: In the scene where we first see Phoebe and Cole when she's about to leave the apartment, you see she is wearing gold and white high heels but as soon as she reaches the elevator she's wearing black boots.
We're Off to See the Wizard - S4-E19
Visible crew/equipment: After Phoebe tells Cole she's pregnant she leaves in the elevator, and when it cuts to Piper, Paige, and Leo we can see the crew's grey mat on the floor under Piper and Paige, then in two following shots (from the same angle) the red T-mark is visible on that mat, at Paige's feet. (00:07:45)
We're Off to See the Wizard - S4-E19
Other mistake: Leo tells Phoebe that fire throwing is an upper level demon power, but we know Phoebe had that power in her past life, Piper even reminds her of this earlier in the episode.
We're Off to See the Wizard - S4-E19
Continuity mistake: When Leo arrives to tell the sisters about the wizard, Phoebe's hands change position between shots. (00:29:55)
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.