Thanks for Clarifying Lance.
Was there any errors in the event log during the staging? This is definitely odd behavior, i've had no problems doing exactly what you are doing before.
Can you run a test for me? Create a user on the Live site, make sure it's assigned to the site, then check the Staging module on the live site. You should see the staging task, hit the Eyeball icon to investigate it, and can you either try to screen shot the information there and get it to us or just take a look? On the bottom you should see a list of related items that also will 'push' with the user and i want to see if the User Site information is in there.