if I change my MAIN site (ipstenu.org) to UTC-0, that changes as well. I wonder if that's a holdover from the old 'first site was main site' days? Try changing that.
Worked flawlessly. So, next question: where would be the best place to document this behavior? (I tried a general Google search, and a Google site-search of the Codex, and couldn't find it.)
If I can find the right place to link (or update) the Codex, this one will be resolved. Do you know the right place in the Codex, or should I maybe ask the wp-dics list?