I have had problems reading RSS feeds, and for the longest time I thought this was due to problems with a User-Agent string making the feed software "hide" entries from the "SimplePie" agent. (There's a post about that as well...)
However, I've now begun to suspect that WP-o-Matic does not handle ampersands (&) in the RSS feed URL that well.
I suspect the RSS call contains
& entries instead of simple
&-signs, and given that the feed URL then is incorrect, I get the wrong type of RSS feed sent back.
I haven't been able to confirm this fully, but feel free to check into it, as things stand now WP-o-matic fails for half of my feeds - which is a shame for an otherwise quite nice plugin!