Usage of DCAwareRoundRobinPolicy with an empty constructor or passing of a null data center does not necessarily set the local data center to be the DC of the first seed node.
It looks like it chooses the DC of the first node in some Hash object after adding all discovered nodes.
Thanks for reporting this. This is the same issue as JAVA-496, which will be fixed in 2.0.7.
Sorry for not addressing your ticket first, I hadn't had time to investigate it, the other ticket got my attention because it outlined the source of the bug in the code.