fetch_rss not parsing feedburner feed with extra directory

I am updating my CommentLuv plugin so that it can parse more types of feeds, it’s working with almost everything I throw at it.

when a feed location redirects to a feedburner link, it works fine if the feedburner feed has the format https://feeds.feedburner.com/username

but, some people have something like
https://feeds.feedburner.com/username/uvWD

if that is the case, the fetch_rss() function doesn’t parse the feed, I’ve tried the magpie function on my own pc and it fetches fine but it doesn’t do it from within wordpress (2.1 – 2.3) when the feedburner link has an extra bit after the username

any ideas why?