[Dovecot] Password auth scheme question with mysql

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