<partial-response> XML shown as plain text after ajax redirect on security constraint in WildFly

I've got this weird problem with ajax redirect on a security constraint:

When an ajax call is made (by clicking on a sortable p:dataTable column or when a p:poll triggers) on a role-secured page after my session timed out, a <partial-response><redirect-url=... XML from OmniFaces is shown on the screen.

When I remove OmniFaces, the ajax calls seem to fail silently and I don't get the XML shown.

Security is configured as following in web.xml:

<security-constraint>
    <web-resource-collection>
        <web-resource-name>Pages</web-resource-name>
        <url-pattern>/*</url-pattern>
    </web-resource-collection>
    <auth-constraint>
        <role-name>user</role-name>
    </auth-constraint>
</security-constraint>

<security-constraint>
    <web-resource-collection>
        <web-resource-name>Resources</web-resource-name>
        <url-pattern>/javax.faces.resource/*</url-pattern>
    </web-resource-collection>
</security-constraint>

<login-config>
    <auth-method>FORM</auth-method>
    <realm-name>myRealm</realm-name>
    <form-login-config>
        <form-login-page>/login.xhtml</form-login-page>
        <form-error-page>/login.xhtml?error=true</form-error-page>
    </form-login-config>
</login-config>

<security-role>
    <role-name>user</role-name>
</security-role>