Following up my earlier jihad, after discussing it a bit with Martin of the khymos food nrrd blog, then doing some investigation when it happened again on Rozie's blog it appears that it's Bloglines that is the problem, not the RSS. At least as far as I can tell. The RSS seems innocuous enough, yet Bloglines marks everything after the post that's actually new as "updated" with the same datestamp.
I've written a note to Bloglines themselves reporting it. Hopefully they'll fix it, otherwise I'll have to find another aggregator. That could be painful.