Silent Cross Site Redirection

Hi,

Recently deployed an Exchange 2013 SP1 server into our existing 2010 SP3 organisation.

I've set the Silent redirect option on both CAS servers

Set-OWAVirtualDirectory -Identity "CAS2010\owa (Default Web Site)" -CrossSiteRedirectType Silent

Set-OWAVirtualDirectory -Identity "CAS2013\owa (Default Web Site)" -CrossSiteRedirectType Silent

Problem is that the silent redirect doesn't work if you go to CAS2010 URL and login you get the Redirection splash page where you have to click the link to the CAS2013 URL and login again. 

If you go to the CAS2013 URL and login to a mailbox that resides on the 2010 box it silently redirects you.

I have the same authentication settings on both Virtual Directories

Any ideas?