When working with an external (second) monitor connected to a notebook via a docking station the display of dialog boxes in KDE applications like dolphin, kontact, kdesu and others gets completely gabled and distorted. This only occurs when an external monitor is connected using the notebook display alone everything is fine. Neither, killing and restarting plasmashell nor restarting the affected application cures the problem. The problem occurs with both render engines (openGL and XRander).
It also makes no difference if the second monitor is used alone (notebook display switched off using xrandr) or in combination with the notebook display (both displays activated) to form a common desktop. The problem also shows up when rebooting with the second monitor already connected at boot time. Actually the dialog boxes functionality works: if suddenly selecting the correct option in pull-down menus leads to the correct behavioral only the display is distorted.

Reproducible: Always

Steps to Reproduce:
1. connect external, second monitor to system
2. activate second display or boot with second display connected
3. work for some time (some hours) and suddenly display of dialog boxes get distorted

Actual Results:  
Completely distorted display of dialog-boxes that makes the system completely unusable and needs KDE stop and restart to be cured.

Expected Results:  
Correct display.