One of the annoyances I've been finding in Exchange 2013 during migrations is that when an administrator with a mailbox in Exchange 2010/2007 attempts to access Exchange Control Panel to administer, they are redirected the the older version of Exchange 2010. This happens because Exchange looks up where the user's mailbox is and assumes that you want to access the server where the mailbox is located.
Fortunately, there is an easy fix for this. Append the url with ExchClientVer=15 to force it to stay on Exchange 2013. For example: