This isn't a new bug I'm afraid.
I first noticed it shortly after my work on Antioch Remastered 2.0 was done (which had a ton of Conversations). I couldn't have finished my with with the bug intact, so it must've been after that.
So I guess, as early as patch 3.9.0 (which was in mid-December, according to Liquidpedia).
Also I'm a PC user, so this isn't just a Mac issue for once.
You can still find text entries from conversations via the Text editor, but stay away from conversations in the Data and Trigger editor.