Copy & paste text in same file suddenly auto-converts to outlines! What changed?

I'm using Illustrator 28.6 on a 2021 MacBook M1 Pro running macOS 14.5.  And sometime in the last week or so, when I copy a text object and then paste it in the same file (either on the same layer or a different layer), for some reason the text is now auto-converted to outlines.  If I select some text in a text object, and then create a new text object and paste the text into that object, the text pastes as expected.

I've never seen Illustrator do this before, and except for Illustrator having updated itself 12 days ago, I can't think of any other change that should cause it to happen.  I've played around with preferences and can't find anything that changes it.  I have rebooted my computer, to no effect.  Does anyone have any idea what might be causing this, or what I can do to fix it?  I'm attaching a simple file showing what happens (I tried an Illustrator file, but it was rejected saying that the "content type (application/postscript) does not match its file extension" even though it was a .ai file; hopefully the PDF version comes through).