I haven’t seen this one before…

    <copy todir="${dirs.build}/etc/" overwrite="true">
      <property name="nginx_fstab" value="#"/>
      <filterchain>
        <expandproperties />
      </filterchain>
      <fileset dir="${dirs.files}/debian/etc/">
        <include name="etc/network/interfaces"/>
        <include name="inittab"/>
        <include name="rc.local"/>
        <include name="sysctl.conf"/>
        <include name="fstab"/>
        <include name="vz/conf/777.conf"/>
      </fileset>
    </copy>

If I remove:

<property name="nginx_fstab" value="#"/>

it works OK.