That is same build# of my Safari and as today's posts on this weirdness indicate: I STILL SEE the "replies" in their proper hierarchy -AND- duplicated! above
(as 'newer') with each reply, now a Parent: properly shifted-left towards LH margin.

I haven't yet tried using one of these Dupes in a Test, adding a reply.. maybe try that next just to see if the weirdness morphs into another clue.
(Will it also fill-in below the real-Parent of that wayward listing .. or Not?)

OK, Boffins: W.T.F. dropped [;] Might account for such a clusterfuck, Hmmm?
(Could not even roll-back to previous V. Safari; Gawd-only knoze what-Else? ..was cobbled-up in OS-X bug-fix: to make THIS V. sorta- kinda- Operate.

Now THERE"s {{sob}} "the heartbreak of psoriasis Irony" when the monolith that is Apple Oversight is even less accessible/responsive than the turgid Microsoft Knowledge "Base" ever Was!
EH?