Ooh, OK, it told Miriam to be quiet, too. I'm guessing there's some latent directory in the constructs to make sure passersby in the hallway aren't too loud. So that Bellwether must've been a construct the whole time. Maybe the illusory disguise just doesn't contact things if the original thing or person doesn't?
Like, say I try to disguise myself as Shaq and then try to walk through a normal sized door without ducking. The disguise would just phase through the top of the frame. But if I try to disguise myself as another 6 foot tall person and walk into a wall, I'd still just run into the wall like normal.