[horde] Passing Auth from Horde Group to IMP failing

[horde at corwyn.net]

CentOS5 running postfix, dovecot. Postfix maintains accounts in 
mySQL. dovecot imap/pop authentication works to mySQL. Currently 
using custom SQL queries in Horde > Authentication.  The queries at 
least appear to be right, as I can log into horde using an account 
set up in the mySQL database. I can log in (via command line to IMAP) 
to dovecot/IMAP.

I have edited imp/config/servers.php and set 'hordeauth' => 'full' so 
users only need to login once and Horde then passes authentication 
data to Imp   (http://oli.lugh.ch/horde-workaround.org.html)

If I change horde authentication to use IMP, then logging into horde 
also logs into IMP. However, What I would like is to be able to log 
into horde using mysql, and have it automatically authenticate to IMP 
/ My Mailbox.  What currently happens is that I can log into horde, 
but I still have a link to log into My Inbox. Selecting that link 
means I have to log in again (same user ID and password).

Besides the change to the IMP config, is there something else that 
needs to be set?

thanks!

Rick