Actually, a little more searching found this bug, which is a duplicate - but does identify the problem as one with gnome-screensaver and discusses some work arounds and possibilities of fixing.
https://bugs.launchpad.net/ubuntu/+source/gnome-screensaver/+bug/93466 -- Do not detect Mouse activity on Second screen while on Dual Desktop Configuration https://bugs.launchpad.net/bugs/96440 You received this bug notification because you are a member of Ubuntu Desktop Bugs, which is subscribed to gnome-screensaver in ubuntu. -- desktop-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
