The way QMainWindow handles dock widget separators is a bit evil. They are real QWidgets, added as direct children of the QMainWindow, but painting and mouse interaction is handled by a hook into the QMainWindow events, via QMainWindowLayoutSeparatorHelper::windowEvent(), which is called at the start of QMainWindow::event(). For reasons unknown, we also raise() these separator widgets, which means they are always at the top of the child window stack of the main window. This is problematic for the situation when a QToolBar has an expanded overflow-menu, which is also raised(), but where we end up raising the separators on top of the toolbar again. As a result the toolbar gets leave events when we hover one of the separators, even if the toolbar menu is overlaid the dock area, resulting in the menu closing. We don't see this visually, as the separators are drawn via the hook mentioned above, which happens before QMainWindow draws any of its child widgets, like the toolbar. Fixing this requires us to selectively place the separators below any expanded toolbar each time we raise a separator, so that we respect the request of the toolbar to be on top, while still ensuring that the separators are above any of the dock widgets. Unfortunately the QMainWindowLayoutSeparatorHelper hook also processes mouse move and click events, resulting in the cursor changing shape when hovering the separator, even if the toolbar menu is over it. To fix this we amend the logic of finding a separator widget based on the mouse event position to also querying the QWidget childAt() function, and if we are over a tool bar, we bail out instead of looking for a separator on that position in the dock area layout. As the special separator logic in QMainWindow is conditioned on the style returning 1 for QStyle::PM_DockWidgetSeparatorExtent the test checks for this, and skips if another style is in use. So far only the macOS style is affected by this. See the original change in fba33a6bbc09bb278df75829d8d705863d40a6a3. Fixes: QTBUG-124733 Pick-to: 6.8 6.5 6.2 Change-Id: Ifc741336bd9725ef0fea9f0474e27b7481f3a183 Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>