Huh. There’s something a little weird going on here, yes. I can get both to happen, which is not quite right…
Select the text you want to use for the synopsis, even multiple paragraphs, etc.
Click the “auto-populate” button in the inspector
For me, doing it directly like this does work. However if you click in the synopsis first, or otherwise interrupt the action, then you only get the first paragraph. So I’ve noted that as a bug, but meanwhile let me know if you’re still not able to get it to work.