ah I was also a little bit afraid of a bug.Looks like a bug to me. The Room Manager content should be kept in sync with the room assets being added or removed. Is this a new 2.3 project, or imported from 2.2.5?
If it is a "big" project you would rather not start from scratch, you could try downgrading 2.2.5, import project, upgrade to 2.3, and open imported project and see if it makes a difference. It's probably what I would do, but no idea if it makes or is supposed to make any difference. Just figure it is worth a try given the project structure overhaul between 2.2.5 and 2.3.