My external monitor is located above my notebook monitor. Notebook is configured main screen. External monitor is frequently docked and undocked (each time I leave my desk and take the notebook with me for a meeting). When undocking my external monitor, the windows that were located on that screen are moved to the primary screen but located such that only some lower corner of the window is accessible.
I Believe it's the same issue as https://bugs.kde.org/show_bug.cgi?id=479694
Indeed, though this one is older so let's use it as the master bug.
*** Bug 479694 has been marked as a duplicate of this bug. ***
Actually it looks like this is more like Bug 452118 which was supposed to be fixed in Plasma 6, so maybe not. *** This bug has been marked as a duplicate of bug 452118 ***