[Dovecot] Password auth scheme question with mysql

[Ed W]

Hi, I have a current auth database using mysql with a "password" column 
in plain text. The config has "default_pass_scheme = PLAIN" specified

In preparation for a more adaptable system I changed a password entry 
from "asdf" to "{PLAIN}asdf", but now auth fails.  Works fine if I 
change it back to just "asdf". (I don't believe it's a caching problem)

What might I be missing?  I was under the impression that the password 
column can include a {scheme} prefix to indicate the password scheme 
(presumably this also means a password cannot start with a "{"?).  Is 
this still true when using mysql and default_pass_scheme ?

Thanks for any hints?

Ed W