Visible crew/equipment: When Claire runs away from Bob after he calls her "Ms. Bennet", you can see Bob's shadow and another person's shadow on the ground. Since no one else was standing next to them, it has to be a crew member, most likely a camera man based on the odd shape of the shadow.
(Volume Two: Generations) Four Months Later... - S2-E1
Visible crew/equipment: S02E01 "Four Months Later". As the samurai warriors are about to engage the attack, a close-up shot of Hiro turning around reveals the white screen reflected in his glasses.
Visible crew/equipment: When Mohinder, Sylar, Maya and Molly are at Isaac's old flat (now Mohinder's lab), as Mohinder and Sylar walk down the stairs, you can see the moving camera crane reflected in the glass behind them.
Chosen answer: Because he's an idiot. From the story point of view, they needed the vault to actually be physically open so that the release of the virus would be a credible threat. Unfortunately, this required that Peter conveniently forget that he could simply walk through The Wall and use his telekinesis to tear the door open instead. Peter's increasingly large arsenal of abilities, where he ended up having pretty much any ability required for any situation, led to a situation where it became necessary to either have Peter apparently forget that he had a given power, as with the vault door scene, or become naively trusting, as with his refusal to scan Adam's mind to confirm his good intent. This problem, which simply made Peter look increasingly dumb as the show progressed, may well have been a key factor in the decision to severely reduce his ability during season three.
Tailkinker ★