Yes, this is normal and nothing to worry about. If both receivers were bound to that transmitter, then both of them can be controlled AT THE SAME time by that transmitter, even if they were set up on different planes. There is on one radio on the market that will differentiate between which model you have selected, and it's not Futaba (JR/Spektrum to be exact).

This is nothing to worry about. You just need to ensure you have the correct model selected before you fly (something that pilots have had to do since computer radios hit the market)

Ken