iTunes U Not Updating XML Collection

In September, we added the SEI podcast collection to CMU's iTunes U site. In October, we think it stopped working due to some odd characters in the feed. The characters have been removed for a couple of weeks now, and iTunes U hasn't picked up the new episodes yet. Do you know what we have to do to fix the problem?

Here is the podcast: https://itunes.apple.com/us/itunes-u/software-engineering-institute/id566573552? mt=10

Here is the XML (looks valid to us): http://www.sei.cmu.edu/podcasts/files_podcasts/itunesFeed.xml

Thanks,

Steve