With nested vertical tabs enabled, closing a parent tab currently shifts the first child up to replace the closed tab. It would be more natural for all children of the tab to be promoted up rather than just the one.
Here is how it currently functions:
Here is how I am proposing it to work:
Tab 1
Tab 2
Tab 3
Tab 4
Tab 5
↓
(Close tab 2)
↓
Tab 1
Tab 3
Tab 4
Tab 5