Initially reported here: https://launchpad.net/ubuntu/+source/xorg-server/+bug/84662 After doing some checking, it appears that the Xnest server isn't receiving mouse motion events when the cursor is moved normally. This seems odd to me, because it's certainly registering for them (hw/xnest/Pointer.c:xnestPointerProc). I've been doing a bunch of tracing and if I change: attributes.event_mask = ExposureMask; to: attributes.event_mask = ExposureMask | PointerMotionMask; around line 91 of hw/xnest/Window.c, the mouse motion events seem to start coming in normally. I'm finding this a bit confusing, since I would expect that all we should need is to register for such events for the original Xnest window? I checked the logs, and it doesn't look like Xnest has been touched in a while. I'll look into this further tomorrow, but I thought I'd file the bug now so other people can comment and/or look into the issue.
I'm an idiot. There is no problem with Xnest: the problem is entirely localized in gnome-screensaver, which seems to be invalidly watching for mouse motion events. Filed a new bug here: http://bugzilla.gnome.org/show_bug.cgi?id=412486 Marking this one as invalid.
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