If you have hide background enabled and open Dressing Room first time (not inspecting another player or inspecting an item) you load or reload the game the background seems to work as intended as this screenshot show:

If you for example inspect the appearance of an item like this screenshot below, the background turns completely black instead of being integrated in the frame: (edit: you just have to switch outfit and the background turns black immediately)

Opening dressing room again as first step still shows black background until /reload:

Any updates on this issue? :)