Ad Blocks don't display ads on Rewrite 301 http:// to http://www

I want to implement the following rewrite rule in my .htaccess file to always load my site using www. This apparently improves search engine results by eliminating Google from seeing duplicate content.

RewriteCond %{HTTP_HOST} ^example\.com$ [NC]
RewriteRule ^(.*)$ http://www.example.com/$1 [L,R=301]

When I implement it image ads are not appearing in ad blocks. The ads are visible if I view them in their main ad node. Not sure if they would display in a page or story node (i.e. embedded in content) because I'm not using that feature. The blocks themselves do appear but minimized, such that the ad that would normally appear there wouldn't fit.

Not 100% sure this is a bug, but all other functionality on the site seems to work... didn't do exhaustive testing, however.