OK, after some looking at it a bit more, I noticed the following:
1. From root/home menu, all appears correct, but any submenu items selected have the issue previously reported.
2. What I didn’t notice before is that the menu is drawn, then the page is redrawn again with the menu collapsed and the issue with the error remains in the content area.
I’m wondering if it is a plugin compatibility issue where one plugin isn’t playing along nice with the others.