When you send a test with personalization, it will select a random subscriber from the list to test with, see http://cm.d.pr/112do/5RYqYhnP
You can select another random subscriber, but it will only give you a list of 3 possible addresses to test with. This would be why you could send multiple tests to tiensin@xxxx.com and receive a different name each time.
I hope that clarifies things for you! Let me know if you need anything else. :)