Sure enough, changing www.jcomeau.com to an A record solved the problem.
Immediately. WTF? The record never even got cached. It's as if the query were
never even made. On my server, the dig query still shows the
CNAME, with another 8 hours till the record expires.
last updated 2013-01-10 20:47:22. served from tektonic.jcomeau.com