AI Text to speech not updating closed captions

When I create a new AI text-to-speech file it adds captions just fine. *

But when I go to update that file on the timeline, even with the "generate CC" box checked, it still has the old captions.

If I delete the existing captions, re-generate the audio with the box checked, and save, no new captions appear.

What can be done about this?

* Also, the AI generation doesn't honor SSML very well. I can't correct its pronunciation of certain words without writing the prompt phonetically, then manually changing the CC every time I update the script.