[horde] IMP not displaying folders other than INBOX

[Carl Wilhelm Soderstrom]

imp-3.2.8
horde-2.2.8
installed via Debian packages.

This worked fine for quite some time, but now, IMP isn't displaying the IMAP
folders other than INBOX.  They do not appear in the folder management page,
nor in the drop-down list of folders in the upper right corner of the
screen. 

They definitely are still available:

hostname:~# telnet localhost 143
Trying 127.0.0.1...
Connected to localhost.localdomain.
Escape character is '^]'.
* OK Courier-IMAP ready. Copyright 1998-2001 Double Precision, Inc. See
COPYING for distribution information.
. login chrome XXXXXX
. OK User logged in
. list "" "*"
* LIST (\HasNoChildren) "." "INBOX.spam"
* LIST (\HasNoChildren) "." "INBOX.sent-mail"
* LIST (\HasNoChildren) "." "INBOX.Trash"
* LIST (\Marked \HasChildren) "." "INBOX"
. OK LIST completed
. logout
* BYE LOGOUT received
. OK Completed
Connection closed by foreign host.

I note that even if you create the subfolders through the webmail
interface, you still can't see them.

The only thing that changed about the time this stopped working, was that
Postfix was upgraded (which should be *completely* unrelated). None of the
configuration files changed at that time (I've looked at ones from backups).

Any ideas what might cause this to happen? 
Any ideas how to fix this? (Short of upgrading to horde v3 and imp v4, and
I'd rather avoid that pain for a while if I can).

-- 
Carl Soderstrom
Systems Administrator
Real-Time Enterprises
www.real-time.com