Same model.ini on 2 DEVO 10 = fixed ID problem

Hello.
I just stumbled on a strange problem with the DEVO protocol.
I have a black Devo 10 with deviation 4.0.1 (public release).
I just bought a white DEVO10 and installed deviation 5.0.0 (public release)
I copied my model.ini files (wich have all a fixed ID) on the new transmitter, .

The funny thing is that on the new transmitter, the fixed ID doesn't work (no binding), I first have to cancel the fixed ID (set on the black DEVO 10) and to set a new fixed ID so the binding occurs.
Of course the model.ini files that work now on the white DEVO 10 don't work anymore on the black one !

It's not a big problem for me, but I would like to understand why I have to set a new fixed ID ?
Is it because of the different versions of deviation ?
Or may it be that there is an "algorythm" wich takes in account a chip serial number or such ?

Thank you if you have some information.

Roland

afaiui there is as you thought a that takes into account the chip serial number as well as the number set in the model ini, this is a safety measure

The tx also has it's own id number. that number is also used in the fixed id binding.
However, you can give the tx an id number in the hardware ini. if you give both your tx's the same number you can control your models with both tx's, while using fixed id binding.
just above the module section, enter:
txid = ********
where * is any number.