The MultiViews option is probably causing this issue. This should be removed. MultiViews (part of mod_negotiation) will attempt to internally rewrite a request for /file (where some /file<.ext> exists on the filesystem) by testing the various files found in that directory and will serve the file that matches the appropriate mime-type. This happens before mod_rewrite has a go and can result in a conflict (since you are trying to do a similar thing with mod_rewrite).
Options Indexes FollowSymLinks MultiViews
