If this was on nvidia back before nouveau, I can believe it. nvidia's drivers have never supported xrandr, so you need to do everything through their proprietary tools. My thinkpad hotplugs displays with no trouble at all these days, but I vaguely recall having trouble with nvidia's drivers about five years ago.
Fantastic; I'm glad to hear it. I've been using nouveau for the past couple of years because of this issue; sounds like it's time to try nvidia's drivers again.
