G'day Mate,
It's simple really, the GUID code that locks the RX to the TX, is different for each model memory in the TX, there are 20 of them, so the RX that is Binded, Bound, or whatever you call it, to model memory 2, won't work, with model memory 1, & so on.
All you need to do is bind the RX, to the TX, when you put it into the new plane, when you use a different model memory, in the TX.
So in short, if you use model memory no.1, that RX will only work with MM, No.1, so to get it to work with any other MM, you need to rebind it.
I hope that is clear.
Feel free to PM if it isn't.