Horde email interface and User Agent string

[#1]

I was tweeking my User Agent string to actually match my system, and the Horde email interface stopped working.
Specifically, I couldn't get submenus to appear (eg clicking on the + next to Mail wouldn't display the submenu of Inbox, Sent-Mail, etc.) and To: addresses didn't search the address book.
I know it will be useless pointing out that servers must not change the content they supply based on what they interpret the User Agent string as meaning, but what does Horde check in the User Agent string to decide not to perform its functionality?
Ta

[#2]

...and this morning I can't even get into Horde:
Forbidden
You don't have permission to access /imp/login.php on this server.
Apache/2.2.3 (Debian) mod_jk/1.2.18 mod_python/3.2.10 Python/2.4.4 PHP/4.4.4-8+etch6 mod_ssl/2.2.3 OpenSSL/0.9.8c mod_perl/2.0.2 Perl/v5.8.8 Server at webmail.mdfs.net Port 80

[#3]

Unfortunately we've had some issues with the webmail service, there is a service status post at status.plus.net and servicestatus.net which I'm just about to update.