[horde] Specifying a domain

[Glenn J. Rowe]

Horde in currently installed on my server at https://woodvale.on.ca/horde

I currently have an apache virtual domain called https://webmail.woodvale.on.ca
The document root for the virtual domain points to /var/www/html/horde/imp
This is the same place as https://woodvale.on.ca/horde/imp
The purpose of the virtual domain is to point them directly there.

My question is this...  When I access https://webmail.woodvale.on.ca it changes 
the URL to https://www.woodvale.on.ca/horde/imp/login.php?
Horde=026750b01b1e02af3002ce00ed97edb7

Why does it convert back to www.woodvale.on.ca instead of staying 
webmail.woodvale.on.ca ?