I've seen that behavior mainly on the "train-wreck questions", where , I suppose, people want to go back, not because of how good the question is, but rather to see how it turns out.

Also, I imagine some people might be [a bit protective of their votes][1] (not such a good example, as there is only one favorite there), so they might be favorite a question that they liked, but not cast a vote, for whatever reason.


  [1]: http://superuser.com/users/1931/john-t