[ #315441 ] XPath analysis: button doesn't change state in dialog edit control

gistfile1.html

<xh:html xmlns:xf="http://www.w3.org/2002/xforms"
    xmlns:xh="http://www.w3.org/1999/xhtml"
    xmlns:xxf="http://orbeon.org/oxf/xml/xforms"
    xmlns:ev="http://www.w3.org/2001/xml-events"
    xmlns:fr="http://orbeon.org/oxf/xml/form-runner">

    <xh:head>
        <xf:model xxf:xpath-analysis="true">
            <xf:instance>
                <text readonly="false">All the world's a stage…</text>
            </xf:instance>
            <xf:bind ref="." readonly="@readonly = 'true'"/>
        </xf:model>
    </xh:head>
    <xh:body>
        <fr:dialog-editor ref="." id="my-dialog-editor"/>
        <fr:button>
            <xf:label>Toggle readonly</xf:label>
            <xf:setvalue ev:event="DOMActivate" ref="@readonly" value="if (. = 'true') then 'false' else 'true'"/>
        </fr:button>
    </xh:body>
</xh:html>