When some tabs in a QTabBar are hidden, the arrow buttons not always work correct. Example for horizontal tab bar:

1. open several tabs so that at least 3 tabs don't fit in the tab bar.
2. select the last tab (-> the left button is active, the right inactive)
3. hide the leftmost visible tab
4. click the left button 
   • wrong: the tab bar scrolls to the very first tab
   • expecting: the tab bar scrolls to the tab left of the hidden tab

This happens if any tab between the currently visible tabs is hidden.

This might relate to these recently fixed issues: https://bugreports.qt.io/browse/QTBUG-139791, https://bugreports.qt.io/browse/QTBUG-102020