This is a regression. The problems don't occur in 5.5.1 and Qt 5.6.0 but are present in 5.6.1 and 5.7.0.
With this code reordering docks via drag&drop is not possible. Dragging seems to be ok but when releasing the mouse the dock goes back to its original position.
is changed to
reordering works on primary screen and any screen to the right. It doesn't work on screens left to the primary screen. I'm guessing something to do with negative position coords in multi-monitor setup?