EDIT: Apologies, apparently this was already reported 2 days ago here: T1355
I'm not quite sure why this didn't come up in my search query...
Crew member gets spat out on scenario start; also, units are not able to be dragged into this crew position from the outside.
I tried moveInTurret (I think  is the correct index for this position) on init, but no joy.
Tested with all faction versions of the tank. Problem not present in legacy 2D editor.