Created attachment 96725 [details]
The top screen is the second one connected using the hdmi port

When I connect to my laptop the second screen using the hdmi port and set it as primary the windows are covered by the task bar (see attachment).
I'm using the last archlinux packages updated to 19 Jan 2016 (plasma-desktop v. 5.5.3-2)
Following my xrandr status:

$ xrandr -q
Screen 0: minimum 8 x 8, current 1920 x 1848, maximum 32767 x 32767
LVDS1 connected 1366x768+554+1080 (normal left inverted right x axis y axis) 293mm x 164mm
   1366x768      59.37 +  59.97* 
   1280x720      59.00  
   1024x768      60.00  
   1024x576      59.00  
   960x540       59.00  
   800x600       60.32    56.25  
   864x486       59.00  
   640x480       59.94  
   720x405       59.00  
   680x384       59.00  
   640x360       59.00  
DP1 disconnected (normal left inverted right x axis y axis)
HDMI1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 477mm x 268mm
   1920x1080     60.00*+  50.00    59.94  
   1920x1080i    60.00    50.00    59.94  
   1680x1050     59.88  
   1280x1024     75.02    60.02  
   1440x900      59.90  
   1280x960      60.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.08    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    72.81    66.67    60.00    59.94  
   720x400       70.08  
VGA1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)