Twitter Atom feed blank for one user but not another?

I've been pulling the latest tweet via search.atom in Twitter.

$feed = "http://search.twitter.com/search.atom?q=from%3A" . $username_for_feed . "&rpp=" . $limit;

The problem is lately it just started showing no content. I went and look开发者_如何学Ced at different URLs and it isn't showing, only for certain usernames??

http://search.twitter.com/search.atom?q=from:kevinbacon&rpp=1

That works for me.

http://search.twitter.com/search.atom?q=from:zesty_one&rpp=1

Here, both accounts have tweets, and when I add most_recent, it makes no difference, so I can't see how date has anything to do with it.

The search atom feed only goes back 7 days. So if that user with a blank feed hasn't tweeted for 7 days it won't show anything.

There is an Atom feed at

http://twitter.com/statuses/user_timeline/$username.atom?count=200