Or should the two fields be <content> and <content:encoded> instead? (Does <content> even exist?) All the documentation says <description> should be an abbreviated summary, but I see nothing that talks about how to achieve that which MIME calls multipart/alternative.
(Just trusting the text/plain consumers to strip the tags out of the HTML to display it is suboptimal; the two versions should be formatted slightly differently to be most readable.)
Update: Ok, I changed the feed to contain both text/plain and text/html versions. Please try that in your favorite feed reader, and let me know if it screws up. A screw-up would be: it's showing you plain text when it could be showing you HTML.