Misplaced popup menu for reparented combo box

When moving a QComboBox to a different widget, its popup menu is not positioned correctly.

See the attached example: When activating an item in the combobox, the combobox is moved to the second widget's stackedwidget. When you now open the combobox, the popup menu is not visible.

In our use case (with larger and more complex widgets) you notice that the popup menu is displayed at a wrong position - probably the menu's global position is still computed relative to the old parent widget?

Not sure if this is a bug in Qt when reparenting widgets or if we simply use the library wrong...