It's been reported to me that 2.9, and previous releases, don't pick up on
RSS feeds sent with a mime type of "application/rdf+xml". Instead, they
download the XML.
As an example, this one:
If those links don't come out, look here for more:
From what I understand, this is perfectly valid as an RSS feed mime type.
At least 4 independent Feedreader users see this behaviour.