A feed I susbscribe to uses a non-permalink value in the GUID, but RSS Bandit still uses that value as the URL. Here is a copied line from the feed:
"ispermalink" should be "isPermalink" which is probably why RSSBandit isn't respecting the assigned value.
Perhaps either check for both attributes, or allow a per-feed override of whether to use the <guid> as the link when available, or always use the <link> value.
(PS. I will alert the webmaster to fix their feed though).