I noticed you are using a subdomain for horde access and I am wondering if maybe that has something to do with it. Did you install horde to the usr/share folder and then symlink it to your subdomain or did you just set the path of the subdomain to point to the horde folder? Or did you create a new subdomain site and install horde to the new sub site in the document root?
Any chance you can provide a test email account? Not quite sure as to why it would just refresh the page instead of logging in but would help to be able to replicate the problem on this end so I can get a better idea of where to go next in troubleshooting.
Take care of your local Veterans and Community.