ITunes U Sending Different URLs when Retrieving RSS Feed

Question

We have a .aspx page that generates RSS feeds for all of our classes on iTunes U, some of which are private and some public. For the private classes, we're checking the signature iTunes U sends along in the URL to make sure the request is coming from iTunes before giving back the RSS feed for the class (with the correct content type), otherwise we return a 403 status.
The problem we're encountering is that iTunes is sending 3 different URLs when entering the RSS feed address in iTunes.
For example, one of our rss feed URLs might be http://www.sitename.edu/rss.aspx?classid=10 .
iTunes U is sending requests to
http://www.sitename.edu:80/rss.aspx?classid=10,
http://www.sitename.edu:80/rss.aspx?classid=10&time=foo&userID=foo&signature=foo ,
and
http://www.sitename.edu:80/rss.aspx?classid=10&time=foo&userID=foo&signature=foo &time=bar&userID=bar&signature=bar .
The first and third URLs both fail our check. As of a couple of weeks ago iTunes U was pulling in our private feeds just fine, but this week when we put in a URL iTunes U fails to get the feed with an error ("iTunes U could not update the content because iTunes U could not reach the specified feed. Verify the feed specified in the feed URL field is available, and then try again."), presumably because of the 3 different URLs it's sending at the same time. (We haven't changed the way our feed works in that time.)
We're using Type: Feed, Security: None, Signature: Append SHA-256 Signature, Check for changes: Daily, and I'm entering the URL into iTunes U as http://www.sitename.edu/rss.aspx?classid=10 .

Answer 1

Any word on this? The only people that could really check on this are at Apple. From the documentation, it's pretty clear that the only URL iTunes U should be sending is the one with one time, userID, and signature, plus it was working until the multiple URLs started being sent.
We really can't leave off the security check because of copyright issues (students in the class are legally allowed to view the materials but anyone outside is not).