The QTabBar handles scroll events, but doesn't call QEvent::accept on the QWheelEvent*, instead opting to call into the superclass QWidget::wheelEvent, which instead causes QEvent::ignore to get called on the event. This results in events being propagated to other widgets as well, which isn't desirable.

For example, trying to scroll on a QTabBar widget inside a QScrollArea results in the wheel event propagating to the scroll area from the inside tabbar, resulting in both scrolling and the tab switching. Expected behaviour is that the QTabBar accepts the events, preventing the scroll area from scrolling on the same event that the QTabBar is using to change tabs.