@mcc
one time gnome just stopped respecting the concept of having more than one XScreen (the second digit in "DISPLAY=:0.0"), and i wrote red hat to ask them about it (i worked for a company that had a support contract, at the time), and they wrote back "we forgot what that did so we just nuked it entirely, nobody who runs linux uses a random collection of heterogeneous displays anymore, right?"
i feel like i've seen this interaction play out many times in my life now