Padlock on Tab

What does the padlock on the tab do?

If you hover your mouse over a tab, “x” appear on the left side of the tab and a padlock appears on the right. Clicking the padlock locks/unlocks it.

It’s supposed to lock the tab to show only the one top-level item and all it’s children. But the functionality has been broken from day one. Hopefully they’ll get it fixed as it has the potential to resolve some of the angst regarding the way the navigator works.