Exchange 2013 ecp redirects on second site

Hi There

Our Exchange environment compromises of two sites in the same AD.  Each site has 1 mailbox server and 2 CAS servers.  The problem is if I load up the https://secondserver/ecp it brings up the logon page but when we log in with the admin account it redirects us to the account's OWA page.  The OWA is reached through the external name for the firstserver (webmail.domain.com) .

If we log onto the first server via "https://firstserver/ecp/" it brings up the logon page then brings up ECP fine and we can manage all servers from both sites through the ECP fine but if the link between the sites go down we can't access the ECP for the second server at all (just get a "page cannot be displayed" as it tries to redirect to the first server external OWA url).

I've checked IIS and there seems to be no redirect in place that we can tell. DNS seems to be fine (no errors) and both servers have different external URL's set for virtual directories. There's NO exchange 2010 server at all - it's purely 2013.

I've also re-created the ECP directory, this had no effect at all.
I attach a screen shot showing the ecp directory's for all of my servers.  each site starts with either TILE or TELE.

Any ideas?

Regards
Gareth