It looks like the intermediate 301's referer is being passed thru (For example, all links on Twitter get wrapped as a t.co link, and that's what shows up on the server). I'd imagine that analytics being mined are intelligent enough to collapse twitter.com and t.co as the same social origin.

Give it a try yourself: https://twitter.com/vikrum5000/status/256898972478763008 Note the protocol.