Upon attempting to reproduce the issue I was unable to experience the same symptoms when testing Horde. When I accessed webmail via the proxy sub-domain and clicked to load Horde the session allowed me to login to Horde normally and did not redirect to an unexpected location nor did it open to a URL that uses one of the two webmail ports (2095 for non-SSL or 2096 for SSL). This testing was performed using the latest EDGE build of cPanel version 11.25, at the time of writing this build was 11.25.0-EDGE_41121.
Please ensure your cPanel version is the latest for your build tree and that automatic updates are enabled. If using the latest version for your build tree, as seen on our downloads page, and if the issue persists please consider submitting a ticket. The link in my forums signature may be used to initiate a ticket submission.
The following downloads page will show the latest version information for each build tree:
Downloads (#Builds) - cPanel Inc.
If needed, you may perform a cPanel update (or a forced cPanel update) using one of the following commands via root SSH access:
Code:
# /scripts/upcp
# /scripts/upcp --force