I have a link in an html block that links to a page on my site that is not built with concrete5. It is an image gallery postcard viewer that opens in a popup. It used to work fine but now concrete5 adds "index.php" in the link and now it doesn't work.

Here is the html with link:

<p><a onclick="window.open('notices/index.html','Notices','resizable=yes,width=700,height=800,left='+(screen.availWidth/2-350)+',top='+(screen.availHeight/2-400)+'');return false;" href="http://www.pixelfarm.ca/notices/index.html"><img src="/index.php/download_file/view_inline/18/" alt="notices.jpg" width="175" height="239" /></a></p>

The link changes to this:http://www.pixelfarm.ca/index.php/old-site/notices/index.html...
which gives me a 404 not found. This only happen when I'm logged out. If I am logged in the link works fine. It also worked fine before I upgraded.
How do I fix this?