Unable to avoid prompting when starting jabber

[Sean McAfee <eefacm@gmail.com>]

I had the following routine set up to connect to the local Jabber server:

(defun my-connect-to-jabber ()
  (interactive)
  (jabber-connect ... arguments ...)

I eventually got tired of always having to respond "no" to the prompt
"Use anonymous authentication? (yes or no)" when running this command.
I assumed that I was being prompted by yes-or-no-p, and a quick dive
into the Jabber source confirmed this, so I adjusted my command:

(defun my-connect-to-jabber ()
  (interactive)
  (flet ((yes-or-no-p (x) nil))
    (jabber-connect ... arguments ...))

Weirdly, this has no effect.  I still get the prompt.

Anyone have any ideas on why this might be?