When a QDockWidget is currently docked and its widget is closed, the dock widget will remain visible.

However, when a QDockWidget is currently floating and its widget is closed, the dock widget disappears.

It seems that when this dock widget disappears, it does so without having received a hideEvent(). Although the dock widget is clearly not visible, QDockWidget::isVisible() still returns true.

If one were to explicitly call hide() on the floating dock widget when its widget is destroyed, this introduces the problem where any subsequent show() will not have any affect. The dock widget will remain invisible.