[Dovecot] Dovecot auth works when tested with doveadm, but fails with Postfix

[Darren Pilgrim]

I have three postfix 2.9.5 servers: chombo, rush, yoshi.  Chombo relays 
to rush and yoshi for outbound email.  Outbound relay requires SASL 
authentication.  Rush and yoshi run Dovecot 2.1.12 servers with simple 
passwd-file backends.

If I create a new password hash for chombo's user, houseloki, on either 
rush or yoshi:

# doveadm pw -u houseloki -p <password>
{CRAM-MD5}...

Then I add that to rush and yoshi's passwd file:

houseloki at _auth.bluerosetech.com:{CRAM-MD5}...

Then `doveadm reload`, it works fine:

# doveadm auth houseloki <password>
passdb: houseloki auth succeeded
extra fields:
     user=houseloki at _auth.bluerosetech.com

So I add that username and password to the smtp_sasl_password_maps hash 
file on chombo, reload postfix, and then try to relay something from 
chombo, it fails with rush and yoshi logging warnings like:

Feb 19 03:32:33 yoshi postfix/smtpd[75783]: warning: 
chombo.example.com[2001:db8::2]: SASL DIGEST-MD5 authentication failed: 
<really long string redacted>

Rush and yoshi have other hashes in their passwd files, and if I 
configure chombo to use one of those, it works fine.  Those hashes use 
digest-md5 and are at least a few years old.  I tried that scheme 
instead of the default cram-md5, as well as several others, but none 
work.  I've poured over the wiki and man pages, but can't find the problem.

What am I missing?  Why can I not generate new hashes correctly?