emacs 24, nnimap, authenticate fail

[pramble]

I have imap problems since compiling emacs 24.1 after 23.4.2.
Both report gnus 5.13.

I collect mail from two servers. Both say they are running "Cyrus IMAP v2.3.16" 
After the update, gnus/nnimap fails to authenticate with one of them,
     Opening nnimap server on muenchen...failed: NO Login failed: 
authentication failure

The imap buffer just says, "23 NO Login failed: authentication failure"

I am at a loss where to start looking for the problem. My authorization 
information is in a .authinfo file which I have not touched. I can run emacs 23 
and everything works. I try emacs 24 and get the authentication failure.
With emacs 24, it talks to one imap server, but gives me the authentication 
failure on the second.

I looked in the imap buffer.
With emacs 24, it starts with the authentication failure.
Under emacs 23, it says "OK" and negotiates its way to cram-md5.

Under emacs 24, I compared the working server and the uncooperative one. Again, 
the cooperative one says OK and negotiates the next step.
I have put tls-program back to the defaults, but I did try most conceivable 
variations on gnutls-cli and openssl.
How can I see what each version is sending to the imap server ?
Many thanks.