Double aaaauuuugggghhhhhhh! Upon further reading and experimentation, I’ve determined that while it’s annoying, this isn’t the same bug; it’s something to do with mod_mime_magic and extensionless files. The application/xhtml+xml rule actually does work under Apache 2.0 for files named with a .html extension.
Today’s lesson: never upgrade.
I’ve been fighting with mod_rewrite to see if I can convince it to behave the same way as mod_dir, and it’s been almost completely unsuccessful. Things work for a single directory but not in general, and I have no clue why. And to top it all off, there’s a fix that’s been available for over two months, but has never applied to the CVS tree, or even mentioned on apache-httpd-dev. I may yet wind up building my own version.
Oh yeah, the thing that does work, per-directory:RewriteBase /my/directory/
RewriteRule ^$ index.html [N]
OK, as suggested in the bug report
RewriteCond %{LA-U:REQUEST_URI} \.htmlworks. I’m not sure why it didn’t before–neglected to sacrifice a goat to mod_rewrite, I suspect–but it’s in place and seems to be okay.