Valhalley of the Dolls (1) - S6-E1
Visible crew/equipment: When Chris tells Phoebe that Paige erased Piper's memory, Phoebe shouts Paige's name then walks away from Piper, and in the next shot we can see two pink T-marks taped to the floor under the table, where Paige is holding Wyatt. (00:27:05)
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.