I had this problem in 0.28.3 so I went back to 0.28.2 and it's still a problem for me in 0.28.4.
When the RSS parser finds an NZB and downloads it, the log says:
[1/20/2009 7:21:27 PM] [NZB] E:\TEMP\xxxyyy.nzb imported - 0 files
(xxxyyy is the name of the NZB, of course.)
Therefore it never appears in the queue. If I go to the RSS tab and click the file and select "add to queue" I get the same thing. If I open the RSS feed with my browser and get the NZB that way, it imports and downloads fine.
Any idea what's up? I'd rather not have to go back to 0.28.2, but I'll have to if we can't sort this out. I'm using Vista SP1 (x64) and I have no reason to suspect my configuration, since it works great on the .2 revision.