broken permalinks with domain mapping

Using the domain mapping plugin, the home pages of my blogs work fine. But on subdomain-mapped blogs (as opposed to directory-based blogs) all the links are broken. They appear correctly when you hover over them, but all re-route to the generic “not found” page of the base blog.

Using the default permalinks on the subdomain blog works — but any of the “pretty” choices don’t.

Here’s the .htaccess:

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]

# uploaded files
RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) wp-includes/ms-files.php?file=$2 [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ – [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

Ideas?