Flagging itself enforces a 10 minute “can’t edit” cooldown so the user cannot edit the post quickly enough to fit within the grace period – and that’s also assuming the post was flagged to threshold immediately after posting!
(It is a bit odd that it’s shown in the post, as it’s only a link, not a quote. I guess the excerpt is baked in?)
While here is the current post, where you can see in the edit history that everything after the first two sentences isn’t present:
I also just tried it myself, and the same thing happened, the edit history was lost, both revisions show the new content (though I only tested with my admin account so it could be different). (Testing again with a regular user, taking time because of the cooldown.)
We’re on 2.4.0.beta10. Happy to test here if you like.
It is weird that in the referenced post, the revision shows but there is no difference between the revisions.
I am actually able to repro this on try! So I’ll reclassify this as bug.
There is a bug here @eviltrout – looks like a mistake in the revision UI to me, notice how I made an edit here adding the bottom sentence, but I am comparing revision 2 to revision 2 instead of revision 1 to revision 2: