QComboBox extra inter-item spacing in list when style sheet decreases font size on all but the first page of QTabWidget / depends on order of parenting the tabwidget

When a QSS style sheet for the application contains
QWidget

and QComboBoxes exist on a page of a QTabWidget
and that page has index > 0
and the QTabWidget receives its parent through the QLayout (as opposed to having its parent given as a ctor argument)
then the combobox list items are wrongly spaced, throwing the height calculation of the list off, leading to the need to scroll when the items should well fit on screen.

Attached demo project demonstrates this with a dialog that is instantiated in two ways:
1. if 'bug' == true, passes 0 to the QTabWidget ctor, letting the layout set its parent indirectly
2. if 'bug' == false, passes this to the QTabWidget ctor directly

(Jira only allows three attached files per round-trip, so I will attach two more files after creating the issue)