Steps to reproduce:
Start Orion, have some tabs open. The tabs will have litte padding to the left. In one tab, open a child tab (e.g. by command-clicking a link). all tabs are now assigned additional padding so that the vertical arrow for the parent item can be displayed. Close the child tab again, the additional padding will stay even though it is not necessary anymore.
I am unsure what the expected behavior is. As user, I do want to be able to restore the original layout without having to close and open the browser again. Currently it seems that some internal state is changed that I cannot reset via user interaction.
I assume the intention is to let people use vertical tabs without nested tabs. However, it is very easy to accidentally open a nested tab, destroying the intended layout for the rest of the session even when the user closes or un-childs the child again.
This seems like a UI design issue. I would expect to have some checkbox in the Preferences that enable/disable tree view, so that when it is disabled, the padding is never used, and when it's enabled, the padding is always used. Maybe I misunderstand the intention of the initial padding setup.
Orion and macOS:
Orion Version 0.99.109-beta (WebKit 613.1.12), macOS 12.0.1