Inventory insight will attach itself to a Scene if you open the window, which is expected behavior. So at some point you opened the window while placing furniture. It doesn't do that by default.
You can toggle the window by using the hotkey you assigned or /ii toggle. Since that is hard to read depending on the font I will put this in caps but remember you have to use the command in lowercase in game.
If this window does not close using either of those methods while you are trying the place furniture then exit the game and from the SavedVaraibles folder delete the 'IIfA.lua' and then open the game and log in.