proxy_store help requested

[nginx_newbie_too]

OK, I just tracked this down to whether the proxy_pass value refers to a
load-balancing upstream collection (as I'm doing above) vs. a hard-coded
reference to one server.  So, if I change the proxy_pass config value to
refer to http://download.foobar.com instead of http://download_servers,
everything works.

Is this a known limitation, or a bug that I should file?

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,248241,248244#msg-248244