.htaccesss

I'm having a problem with htaccess

RewriteEngine on
RewriteCond %{HTTP_REFERER} !^http://www.mydomain.com/.*$ [NC]
RewriteCond %{HTTP_REFERER} !^http://mydomain.com/.*$ [NC]
RewriteRule .*\.mp3$ download.php
RewriteRule .*\.zip$ download.php

now what happends is when someone click on a link to an mp3 files it opens download.php which has a link to the file and you can download. which works fine.

but when someone downloads a .zip file it brings it to download.php which is fine but when clicking on that link the same page (download.php) reloads.. i don't understand why this would happen as why should anything different happend with a .mp3 or .zip?

download.php contains this:
">

<? echo $REQUEST_URI ?>

which just gives the link to the file.

hope someone can help

thanks