Trailing slash getting added to .css files?

This is a multi-site instalation set to subdomains, but uses the domain mapping plugin to override with real domains. There is no .htacess file, the rules are in the vhost.

Requests to URLs like:

http://www.site.com/wp-includes/js/jquery/jquery-migrate.min.js?ver=1.2.1

Are getting 301 redirected to:

http://www.site.com/wp-includes/js/jquery/jquery-migrate.min.js/?ver=1.2.1

(note the slash before the question mark). This is clearly wrong and is breaking the stylesheets, but I don’t see any rule that would be causing this behavior.

These are the rewrite rules in the Apache VirtualHost block:

RewriteEngine On
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]

RewriteRule ^(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^(.*\.php)$ $1 [L]

RewriteRule . /index.php [L]