I went through the checkout process as another user (I have an admin account). Then when I was going back through the checkout screen as myself I had their shipping information as the Shipping Address. I could change it of course, but I'm not sure why I would have their shipping info in my cart checkout.
Shipping addresses, among other things, is tied to a sessionId. This is stored on a cookie in your browser.
If you log in as a different user, using the same browser, then information from the last time you logged in (not matter as who) will be used.
Closing as not a bug, but really, really confusing for users and developers.
Was this done from the same browser and same machine? I can't replicate from two seperate browsers.
Per Perlmonkey's request... same browser same machine.
Closed per the boss as this is how authent works for now.