It is revealed that Angelique is in the room when it changed. Why did she not go to regular time? I recall this from when I first saw this thinking it was not right.
In a magical environment, absolute consistency is not to be expected. Everyday rules of cause and effect don't necessarily apply.
You might as well ask, why didn't the PT furniture stay in the Room, when it changed to RT? Both versions of this room exist concurrently at all times, as with every other room and place and thing in both universes, if you're wondering where PT Ang was while the Room changed. The PT Room continued on unchanged through the whole thing, from Ang's perspective. The channel was changed, for an observer in the hall