Microsoft Exchange 2013 iApp - Can't login to OWA or ECP if more than one server is active in pool

To know that you're truly bypassing BIG-IP you'll need to confirm that you are hitting more than one server. I'm guessing you'd need to disable DNS caching on your client as well to allow this: http://support.microsoft.com/kb/245437/EN-US

You can look at the response in HTTPWatch or Fiddler. There should be a header named "X-FEServer" that should change part of the way through your session. This indicates which CAS you are connecting to.

If it is really working, I suggest reconfiguring the iApp for SSL bridging mode. When you connect directly to the server you are encrypted all the way through; by turning on SSL bridging you'll also be encrypted from the client to BIG-IP to CAS. You shouldn't need to change anything on the CAS since encrypted connections are expected by default.