I had the same problem but no answer as to why. I solved it by assigning another device in the PUC list and using the learning function in the Apple TV to learn that devices commands. That solved the problem for me. It also allowed me to add 9 extra buttons to the Beo 5 for control of the apple TV, such as play,fast forward, next track etc.
Beovision 7-55 with Beolab 7-4, 9s and 4000s
Beovision 10-40 with Beolab 1s and 6000s
Beosound 1, 5, 2000, and 3000
Beotime, Beotalk, Beocoms