The mirror part only works when you switch on the airplane mode. It's actually make sense, as you said, once it switched to airplane mode, the connection cuts off.
This single direction function looks a bit silly, but it make my life easier. Sometimes when I want to switch all my devices to airplane mode, I realise that the seat belts makes me a bit hard to pull out the 6+. Also, one switch, and then all safe, which is actually not bad at all.
On the other hand, due to system limitation, we must switch off airplane mode one by one. There is no other choice yet. But in my experience, It's actually OK, because by that time, I usually just leave my seat and stand up, very easy to pull the phone out. And also, this action serve as a final check that I do carry my phone, but not leave it in the seat pocket.