QTabWidget pane styling with style sheet does not position tab pane correctly

When styling a QTabWidget's frame the position of the frame relative to the tab bar varies depending on the base style (and usually therefore the platform) - instead of being fixed by the CSS rules which appears to be the intention.

In Qt Designer applying this stylesheet to a tab bar should cause the bottom of the tab bar and the top of the bar bar frame to just touch:

QTabBar::tab

QTabWidget::pane

Instead, the bottom of the tab bar descends below the top of the tab frame slightly. The effect is worse on MacOS.