I have a similar problem. I am using XenForo 1.5.0. I have a valid set of feeds. The feeds are setup and preview in the feeder add-on. The feed imports and is posted to the forum. But all new versions of the feed do not import into the forum, they preview as before but will not post, either automatically or through the 'import' button. If I delete the feed and set it up again the feed imports exactly as it should. It seems that the trigger that identifies the feed has changed is not working. The rss that is imported has <pubDate> tags and all seems in order.