On my system, I have the Notification Area, the Volume Applet, the System Monitor, the Clock, and the Workspace Switcher on the right side of my panel going left to right. The Notification Area and the Clock change width from time to time, so perhaps that's what is causing this trouble.
As a workaround, I'm going to try keeping all these applets a small distance apart from each other rather than flush up against themselves and see if that fixes this issue. -- GNOME Panel icons (on right side) move apparently randomly on session start in some situations https://launchpad.net/bugs/44082 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs