cyrus imap real moves but sasl stays put

[Ross Boylan]

I made a virtual machine whose disk was a writable snapshot of the disk
from another VM.  After I changed the hostname, I was unable to login to
cyrus imap until I created a new user in sasldb (with the new real).  It
seems that sasldb kept the realm/hostname with which they were
originally created, but the accounts in cyrus imap moved to the new
hostname.  Could anyone help me understand what was going on?

Here are more details about what I did.  The old vm was vm-lenny00; the
new one was vm-migrate07.

On the new vm, 
# sasldblistusers2
cyrus at vm-lenny00: userPassword
ross at vm-lenny00: userPassword

I tried explicitly qualifying the names I used to login to imap; when
that didn't work I added this line to imapd.conf:
loginrealms: vm-lenny00 vm-lenny00.kvm.lan

At this point the logs indicate I was able to authenticate, but my mail
clients (evolution and mutt) reported they couldn't find a mailbox.

Then I did 
# saslpasswd2 -c ross
which created a ross at vm-migrate07 id in the sasldb.  I was able to login
to imap, using an unqualified "ross" as my username.

So the imap server acts as if the accounts formerly associated with
ross at vm-lenny00 actually belong to ross at vm-migrate07.  In this case
that's convenient, but I'm puzzled why it happened.

sasl 2.1.22 with cyrus 2.2.13 on Debian Lenny.  imapd.conf includes
allowplaintext: yes
sasl_minimum_layer: 0
loginrealms: vm-lenny00 vm-lenny00.kvm.lan
sasl_pwcheck_method: auxprop

No virtual domains options are set.

Thanks.
Ross