E.g., "getRelatedTagsForGroup" returns many (20+) tags for http://www.bibsonomy.org/group/kde/analysis%20people%20sys:relevantFor:kde although only one post is returned having the tags "analysis important information_spreading people tumor twitter".
My assumption is, that the SQL iteration
(<iterate property="tagIndex" conjunction=" OR ">t.tag_lower = LOWER(#tagIndex.tagName#)</iterate>)
is not working. For post queries we never use OR but self-JOINs. There are also other queries that use this construct.