Oddly, when I add a random additional search for any document, I get the behavior I expect when using begins with, in that I am able to see the matched groups in the sidebar:
I now see the groups I expect within the smartgroup in the sidebar as well as the listview:
However, I have to add search terms I don’t want. I’ve tried other search terms and it doesn’t work. It seems to need something added using OR/Any.