Logged In: YES 
user_id=6405

Which backend are you using? Note there's an outstanding bug 
filed against "RDBMS backends can't sort on multilink". I'd say 
there's a good chance you're running into this bug?

The bug is fixable, but the fix will be slow (ie. it'll be done in a 
post-SQL step). I've not had time to address it, since it's not a 
serious bug (IMO :)