screen Mirroring Change Intentional or some OS Bug apple is not aware of?

The screen mirroring is active when you are not using Airplay, it's enabled now for Directly connected Monitors, My 49-inch widescreen now shows up as a Mirror Extended Monitor. This was never the case, if I disable mirroring I can no longer use my Display Port-connected Monitor.

What has happened? some comments state this should have been fixed in 15.2 but persists in 15.4