Glitshes when dragging QDockWidget's out of a floating tab window

Example on how to reproduce the bug with examples/widgets/mainwindows/mainwindow:

• Select the option "Groupped Dragging" from the "Main window" menu
• Drag and drop dock widget so there are at least three of them in the same group of tabs (for example red, black, and green)
• Drag the tab bar of one of them outside to make it floating (for example black)
• Drag away the group of two remaining tabs to make them floating
• Drack back the floating-alone (black) dock widget somewhere back inside the main window.
  => The black dock widget is tabbed with the other instead of being

Another issue: If you have a smal floating tab windows, and will drag one of the tab out and dock it in the mainwindow so it has a different size, you will see a glitch in the tab bar of the floating tab window when the dock widget animates.

Both issues have the same root cause: The dock widget is still in the layout.