EDIT: Try the Magazine Madness theme, it has support for marquees in Detailed view.
You're correct @mitu. Just tried in both Detailed and Automatic views and without videos referenced, the marquees do indeed appear.
For each theme I used that exhibits the problem, the marquee section is under <view name = "video">. Updating the themes, including Carbon, by moving the marquee section under <view name = "Detailed"> works (and would seem to be a more common scenario).
Seems that many themes used Carbon as a baseline and have marquee under the video view section. Easy to fix (or change, if it was what the author intended).
Thank you, as always.