Description of problem: I use KDE on my laptop, but configure an external monitor as my primary monitor when using it at home. When using a single taskbar, KDE was ignoring the "primary" output setting and displaying the panel on the laptop screen even when the external monitor was connected and configured as the primary display, so I had KDE configured to display a taskbar (including the system tray, desktop switcher, time, etc) on both monitors. Since the Plasma 5.5 update, KDE has intermittently decided not to display one or both taskbars (the original problem was not displaying one on the external monitor, currently it isn't displaying the one on the laptop monitor) Version-Release number of selected component (if applicable): plasma-workspace-5.5.0-2.fc23.x86_64 How reproducible: At a rough guess, 1 login in 3 since the 5.5 update Steps to Reproduce: 1. Log out 2. Log back in 3. Actual results: One or both panels have disappeared, or moved to the other monitor Expected results: Panels stay in their original location Additional info: Given the timing, I'm assuming this is due to the Plasma 5.5 upgrade in https://bodhi.fedoraproject.org/updates/FEDORA-2015-0f88189b65 , so I'm going to try to update in https://bodhi.fedoraproject.org/updates/FEDORA-2015-f0aa62dc50 to see if that helps matters.
Updating to 5.5.0-4 didn't fix the problem, even after clearing all plasma and KDE related files from ~./cache and restarting the machine. An additional detail of the symptoms worth noting is that when one of the panels "disappears", what actually seems to have happened is that both panels are displaying on the *same* monitor - this can be seen by right-clicking and removing the panel from the panel options, getting the notification that it has been removed (with the Undo option), but still being able to see the other panel where the removed one was. Moving one of the panels to a different screen edge also reveals that both panels have ended up on the same monitor. However, it's no longer possible to move the panel *between* monitors - it snaps to the boundary between them instead (while staying on the original monitor).
I can confirm this behaviour even with a single panel. The panel is displayed almost at random on one of the two monitor. The only way to surely have it on the correct one is to have the external monitor already connected on startup (at least in my case). Subsequent disconnection/reconnection of the monitor could cause again the panel to move. Killing and restarting plasma doesn't help. Still present on plasma 5.7.1
possibly related https://bugzilla.redhat.com/show_bug.cgi?id=1322724. As stated in this bug report, also the wallpapers are placed at random on the two monitor. The displayed wallpaper seems to not be related with the presence or not of the panel. Also very often, in my case, I get a black screen on the laptop monitor with no plasmoid and no wallpaper (this happens always if the external monitor is connected on startup).
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