I recently installed Manjaro 18.1.4 with KDE Plasma desktop. I have a multi-monitor configuration with 4 (physical) monitors arranged in a 2x2 pattern. Primary monitor is the monitor at lower left. That's also where the application bar is located.
So I have 4 (logical) screens that are arranged in a 2x2 pattern, every screen corresponding to a physical monitor. The setting within the KDE desktop is accordingly. This is working fine, and the screens are where they are supposed to be. In particular, I can drag windows from one screen to adjacent screens.
There are 2 workspaces, as usual, with 2x2 screens each.
My problem is that windows are not opening on the proper screen.
I want all windows to open on the primary screen (lower left) unless they were closed or minimized on another screen. In that case I want them to return to the screen where they were closed/minimized.
If I click on the Application Starter (symbol at lower left of primary screen), the application menu opens on the screen/monitor above the primary screen/monitor (upper left).
Clicking on the application menu (dotted field in the upper right corner) does not result in the menu opening in the same place. The menu opens on the screen/monitor above. However, if I am clicking on an application menu that is visible in the upper screens/monitors, the menu correctly opens on the same screen/monitor.
Pointing with the cursor on one of the icons in the application bar causes some sort of "information display" to pop up. However, these do not show up on the screen/montor that contains the application bar (primary monitor at lower left), but on the screen/monitor above.
Right click on the application bar causes the corresponding menu to show up on the screen/monitor above.
Starting applications from the application bar (such as Dolphin) or the application menu sometimes(!) causes the corresponding window to open on another monitor.
In short: how can I force KDE Plasma to open all windows on the primary monitor?
(I have another test installation of Manjaro with Gnome desktop that does not have all these problems. So I am sure that it is related to the KDE Plasma desktop.)
Thanks for help.