expression validator not playing by the rules

[stanlick]

After chasing a CSS issue around tonight, I discovered the following
validation is not placing it's message in the <s:fielderror /> collection
but rather it is adding to the <s:actionerror />.  Shouldn't the validator
be adding to the field errors when a field name is specified?

    <field name="credential.password">
        <field-validator type="expression">
            <param name="expression">

credential.passwordRepeat.toUpperCase().equals(credential.password.toUpperCase())
            </param>
            <message key="passwordsNotMatching" />
        </field-validator>
    </field>

Scott