[SOLVED] Why does Split not work on nominal data read from csv file?

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<process version="5.2.008">
  <context>
    <input/>
    <output/>
    <macros/>
  </context>
  <operator activated="true" class="process" compatibility="5.2.008" expanded="true" name="Process">
    <process expanded="true" height="654" width="970">
      <operator activated="true" class="generate_data_user_specification" compatibility="5.2.008" expanded="true" height="60" name="Generate Data by User Specification" width="90" x="45" y="30">
        <list key="attribute_values">
          <parameter key="line" value="&quot;a,b&quot;"/>
        </list>
        <list key="set_additional_roles"/>
      </operator>
      <operator activated="true" class="write_csv" compatibility="5.2.008" expanded="true" height="76" name="Write CSV" width="90" x="179" y="120">
        <parameter key="write_attribute_names" value="false"/>
        <parameter key="quote_nominal_values" value="false"/>
        <parameter key="format_date_attributes" value="false"/>
      </operator>
      <operator activated="true" class="read_csv" compatibility="5.2.008" expanded="true" height="60" name="Read CSV" width="90" x="380" y="165">
        <parameter key="use_quotes" value="false"/>
        <parameter key="parse_numbers" value="false"/>
        <parameter key="first_row_as_names" value="false"/>
        <list key="annotations"/>
        <list key="data_set_meta_data_information">
          <parameter key="0" value="line.true.nominal.regular"/>
        </list>
      </operator>
      <operator activated="true" class="split" compatibility="5.2.008" expanded="true" height="76" name="Split (2)" width="90" x="514" y="165">
        <parameter key="attribute_filter_type" value="single"/>
        <parameter key="attribute" value="line"/>
      </operator>
      <operator activated="true" class="split" compatibility="5.2.008" expanded="true" height="76" name="Split" width="90" x="380" y="30">
        <parameter key="attribute_filter_type" value="single"/>
        <parameter key="attribute" value="line"/>
      </operator>
      <connect from_op="Generate Data by User Specification" from_port="output" to_op="Write CSV" to_port="input"/>
      <connect from_op="Write CSV" from_port="through" to_op="Split" to_port="example set input"/>
      <connect from_op="Write CSV" from_port="file" to_op="Read CSV" to_port="file"/>
      <connect from_op="Read CSV" from_port="output" to_op="Split (2)" to_port="example set input"/>
      <connect from_op="Split (2)" from_port="example set output" to_port="result 2"/>
      <connect from_op="Split" from_port="example set output" to_port="result 1"/>
      <portSpacing port="source_input 1" spacing="0"/>
      <portSpacing port="sink_result 1" spacing="0"/>
      <portSpacing port="sink_result 2" spacing="0"/>
      <portSpacing port="sink_result 3" spacing="0"/>
    </process>
  </operator>
</process>