Thanks for that link, PerriP.
This was very telling and clears up, for me, why Penner threw his vote.
I think Penner's tribe would not be happy with him for voting with
Tandang (and his ally Skupin), and voting off one of their own (Jeff), so he voted with his tribe, but made sure his vote resulted in the ousting of his nemesis, Jeff.
Somehow I'm not surprised Jeff is still bitter.