antcontrib foreach executed in parallel does not raise errors

I have the following ant script that I can't seem to find a way to make fail when parallel is set to true for antcontrib's foreach task. Any ideas?

<project name="asdf" >
    <taskdef resource="net/sf/antcontrib/antcontrib.properties">
        <classpath>
            <pathelement location="../lib/ant/ant-contrib-1.0b3.jar" />
        </classpath>
    </taskdef>
    <target name="build">
        <foreach target="exex-subant" param="foreach.dir" parallel="true" maxthreads="4" inheritall="true" list="1,2,3">
            <param name="target" value="build" />
        </foreach>
    </target>

    <target name="exex-subant">
        <fail>test</fail>
    </target>
</project>