Agreed, this behaviour was present in FSX also. My query to LM is why?For what it's worth, it has always been the case and will always likely remain the case that using a complex 3rd party aircraft in your default scenario will lead to significant issues. That's not to say that LM doesn't have a bug here, but always keep one of the default planes as your default scenario and switch it to the plane you want before loading the flight (i.e. you should still load it in the scenario screen). I believe both A2A and PMDG documentation both state this, and things like this are the reason why.
Is it because the more complex aircraft are altering P3D core files and upsetting the applecart, or is there some more complex reason that involves the OS, Sim and add-on?
Either way it would be great if LM and Add-on developers got their heads together and sorted it out, it's been bugging customers for some considerable time!