Drag & Drop Events are lost in floating QDockWidget when AA_NativeWindows = true

See attached Creator Project. Drag inside the the view when it is docked, you'll see the drag move cursor. Undock (float) the view, then drag and drop doesn't work (cursor changes to "forbidden" symbol).

I've debugged quite a while to find the cause, and as far as I can tell the issue is rooted in the way a QWidgetWindow is created.

QWidgetWindow::handleDragEnterMoveEvent looks for the child under the current mouse pos:
QWidget *widget = m_widget->childAt(event->pos());

When native windows are off, m_widget will be the floating QDockWindow, but if native windows are on, m_widget will be the QMainWindow which naturally doesn't find a child at the given mouse pos.

We can currently work around this because we decided to turn AA_NativeWindows off. However, we do use native widgets through qtwinmigrate, so we had to turn on AA_DontCreateNativeWidgetSiblings in addtion to work around this bug.