Not long ago, a user reported an issue using the EPPC protocol to access AirPlay properties of iTunes on a remote machine. To keep a long story short, it doesn't appear to be a bug. The user neglected to incorporate a "using terms from" block. I should have known at the time that this was a likely omission. This is an example how the code should be implemented:
tell application "iTunes" of machine "eppc://user:password@Remote-Machine.local"
using terms from application "iTunes"
set apDevices to (get name of every AirPlay device whose available is true)
end using terms from