I am using KDE 5.18 on my Lenovo X240 running Fedora 23.

This is my typical display setup:

jharting@x240 ~ $ xrandr
Screen 0: minimum 8 x 8, current 1366 x 768, maximum 32767 x 32767
eDP1 connected primary 1366x768+0+0 (normal left inverted right x axis y axis) 277mm x 156mm
   1366x768      60.00*+
   1280x720      60.00  
   1024x768      60.00  
   1024x576      60.00  
   960x540       60.00  
   800x600       60.32    56.25  
   864x486       60.00  
   640x480       59.94  
   720x405       60.00  
   680x384       60.00  
   640x360       60.00  
DP1 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

I am using a standard KDE panel on the bottom of the laptop's built-in screen.
Here's its configuration (I do not configure it manually through the conf. file):
[Containments][1]
activityId=
formfactor=2
immutability=1
lastScreen=0
location=4
plugin=org.kde.panel
screen=0
wallpaperplugin=org.kde.image

I run into an annoying problem when I connect an additional external monitor using VGA output.
I configure displays with:

xrandr --output eDP1 --auto --primary --output DP2 --auto --above eDP1

and the xrandr output afterwards looks like this:

jharting@x240 ~ $ xrandr
Screen 0: minimum 8 x 8, current 1920 x 1848, maximum 32767 x 32767
eDP1 connected primary 1366x768+0+1080 (normal left inverted right x axis y axis) 277mm x 156mm
   1366x768      60.00*+
   1280x720      60.00  
   1024x768      60.00  
   1024x576      60.00  
   960x540       60.00  
   800x600       60.32    56.25  
   864x486       60.00  
   640x480       59.94  
   720x405       60.00  
   680x384       60.00  
   640x360       60.00  
DP1 disconnected (normal left inverted right x axis y axis)
DP2 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 531mm x 299mm
   1920x1080     60.00*+
   1680x1050     59.95  
   1280x1024     75.02    60.02  
   1440x900      59.89  
   1280x960      60.00  
   1280x800      59.81  
   1152x864      75.00  
   1280x720      60.00  
   1024x768      75.08    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   848x480       60.00  
   640x480       75.00    72.81    66.67    60.00    59.94  
   720x400       70.08  
HDMI1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

What happens is that the panel automatically moves away from the laptop monitor to the bottom of the external monitor. 

That is kind of annoying because even with external monitor connected I still keep on using the laptop monitor as well. There's no need to move the panel away.

What's worse is that when I later disconnect the external monitor the panel does not move back to laptop's screen. I am left with no panel and thus unusable UI.


Reproducible: Sometimes

Steps to Reproduce:
1. Have a panel configured on a laptop screen
2. Connect and external monitor to the laptop and use xrandr to configure the screen layout
3. Repeat connecting/disconnecting the external monitor several times if needed

Actual Results:  
The panel either moves to the external's monitor screen and stays there (and does not come back even after disconnecting the external monitor thus making the UI useless) or unpredictably changes the actual screen after some times when the monitor is connected/disconnected

Expected Results:  
The panel should stay at the bottom of laptop screen

Sometimes I can observe the following change in the panel configuration:
-lastScreen=0
+lastScreen=1

but other times the panel moves to the other screen even without this change.

When this happens my workaround is to revert the change in plasma-org.kde.plasma.desktop-appletsrc file and run "killall plasmashell && kstart plasmashell &> /dev/null"