Redirect loop on subdirectory sites

Default multisite code for subdirectories is now in my 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]

No plugins currently. This is a completely fresh WP 3 install. Really strange issue.

This is the vhosts record for the install (with vital info blacked out)

<VirtualHost —.—.—.144:80>
ServerAdmin [email protected]
DocumentRoot /var/www/sub.domain.com
ServerName sub.domain.com
ErrorLog /var/log/apache2/sub.domain.com.error_log
TransferLog /var/log/apache2/sub.domain.com.access_log
</VirtualHost>

I hope this makes sense – We have a WPMU install on the same server using the same domain. Could that interfere and cause this problem (or need a special vhosts setting) even though the subdomain is different?
The WPMU is called later in the vhosts file and uses the subdomains *.domain.com, so it shouldn’t interfere, but at this point, I’m willing to look at anything.

I’m a bit of a novice on httpd.conf, so if there are other settings that I should try, please let me know.

Thanks for your effort so far.

It looks like Multiviews is enabled under Options. Should it be?