I recently setup an Exchange 2013 Server in an Exchange 2010 Environment.
All worked fine, but logging in to https://ex2013.wardvissers.nl/ecp redirected me to the old Exchange 2010 Interface.
If you have this problem, you can add the Exchange Version to the URL using “?ExchClientVer=15″.
So https://ex2013.wardvissers.nl/ecp?ExchClientVer=15 will redirect you to the correct Management Interface.
Note: If the Mailbox of the Administrator account resides on the new Exchange 2013 Server this will be obsolete.
Or you add an extra / add the end https://ex2013.wardvissers.nl/ecp/