I have a UI written in Qt that makes extensive use of dock widgets, primarily so that end users can customize which which docks are available, and how they are arranged.
We recently upgraded to Qt 5.6.1, and the dock widgets can no longer be rearranged on Ubuntu, although they still work on windows and other OS's. When you try to move the docks, the rubber band still appears as usual showing the new location, but when dropped the dock just snaps back into whichever position it started in, which is always tabbed somehow.
After several hours of searching, I think the problem is related to QTBUG-54185, and I'm wondering if there is any way to work around the bug while we wait for the Qt 5.6.2 release which fixes it.
The bug is related to having the AnimatedDocks property disabled. QDockWidget rearranging still works, even in spite of the bug, for dock widgets which are animated.
The problem was that in the code, the main window was setting the dock options manually as
mainWindow->setDockOptions(AllowTabbedDocks);
Since DockOptions are OR'd, what is happening here is that the AnimatedDocks property, which is enabled by default, is being unintentionally disabled. The solution for me was to delete the offending line, since the default options are AllowedTabbedDocks|AnimatedDocks, which is actually what I wanted all along.