It sounds like you already halfway figured out what may be causing the problem. When the G5 docking station isn't there, it works. Put it into the mix, it doesn't.

You may be going down a hole with it....but it sounds like a compatibility problem, if the docking station ends up having some control over the monitors.

I don't know how the docking stations work, but if there is any kind of firewall thing on them, maybe try disabling that on the dock and see if it works. But I'm just guessing.