Undocked panel shifting (sometimes...)

The problem is found when using QGIS software which use Qt for it's GUI. I initially made a bug report on the QGIS side, but I have been told that the problem is with Qt (https://issues.qgis.org/issues/19580)

In QGIS, you can dock and undock panels (Table of Content, Identify Results, Processing toolbox, etc.) and place them anywhere on the screen. In my case, if I put any undocked panel on my secondary screen (or primary screen), it will always shift some 8 pixels to the right and 26 pixels to the bottom the next time I restart QGIS. I have performed several tests to try to isolate the problem and here is how to reproduce it:

-Undock two panels (eg. Layers and Browser), put them anywhere (still undocked and not stacked) but make sure to have a visual reference with the main GUI of QGIS for comparaison.
-Close QGIS and reopen: you should be able to see that both panels are shifted from their original position.

However, it isn't always all undocked panels that are shifted. In an other test with the Processing Toolbox undocked along with the Layers one, the Layers panel shifted and the Processing Toolbox panel simply disappeared! To make it reappeared, I had to redocked the Layers panel (stacked with the Browser) and then reactivate it otherwise the panel didn't want to come back.

I also encountered the panel shifting problem with only Processing Toolbox undocked and the Layers and Browser panel docked...

Finally, during my experiments, on the reopening of QGIS, a few times the main window was reduced in size (maybe a quarter of my screen) and snapped to the top left corner of my screen but with the maximize/minimize toggle still showing as being maximized (by default, my QGIS is always maximised on startup). I suppose I should open a separate issue for that part it never happened to me before except when playing around to test for my panel shifting problem.