I just tested with 0.99.126.4.1-beta and 0.99.126.4.1.8-rc
If the link is opened with command+click, back button is disabled and I can't use any of the back features to close the tab and move to parent.
If clicking a link opens a new tab on it's on (i.e. Kagi search result) then the back button is enabled and going back closes the tab.