Can reproduce this on multiple forums, so it’s not a site setting thing. This occurs outside of the edit window, and refreshing/navigating will cause it to appear.
Hmm so it does seem to, but it requires a page refresh. When you edit the first post using the composer (the edit button under the post) the entire post is refreshed on save.
When you edit the title only (using the pencil button after the title), the first post isn’t updated to show the edit indicator.