The "thin space" is treated as a breaking character in the 1.8.4 betas, whereas it was previously a non-breaking character, such as in the 1.8.3 release.
When I open the attached document in Publisher 1.8.3 release, this is what I see:
But when I open the same document in beta 1.8.4.687, I see the question mark (last character in the frame) has been separated from the word it precedes:
I have only noticed it today in beta 687, but I am sure it goes back to one of the earlier betas, because I have a printed document that was printed some weeks ago with an earlier beta.
Edit: I should have noted that I am on an iMac with macOS 10.14.6.
breakable_thinspace.afpub