Unsure how the 0.29 spec handles this

I ran this in dingus and I’m trying to wrap my head around which indentation is correct. I think the second 3.1 indented item is not correctly rendered.
The indent numbering on each line is what I understand the indentation nest to be, according to my reading of the 0.29 spec, but the 3.1 appears at the base level. I don’t see why 1.1 and 3.1 do not behave the same.

- 1
  - 1.1 two spaces and then the '-' (indent one deeper)
    - 1.1.1
- 2
 - 3 one space slush. This appears correct according to the spec.
  - 3.1 two spaces and then the '-' why not indented one deeper?
    - 3.1.1
    - 3.1.2
      - 3.1.2.1
      - 3.1.2.2
- 4
  <list type="bullet" tight="true">
    <item>
      <paragraph>
        <text>1</text>
      </paragraph>
      <list type="bullet" tight="true">
        <item>
          <paragraph>
            <text>1.1 two spaces and then the </text>
            <text>'</text>
            <text>-</text>
            <text>'</text>
            <text> (indent one deeper)</text>
          </paragraph>
          <list type="bullet" tight="true">
            <item>
              <paragraph>
                <text>1.1.1</text>
              </paragraph>
            </item>
          </list>
        </item>
      </list>
    </item>
    <item>
      <paragraph>
        <text>2</text>
      </paragraph>
    </item>
    <item>
      <paragraph>
        <text>3 one space slush. This appears correct according to the spec.</text>
      </paragraph>
    </item>
    <item>
      <paragraph>
        <text>3.1 two spaces and then the </text>
        <text>'</text>
        <text>-</text>
        <text>'</text>
        <text> why not indented one deeper?</text>
      </paragraph>
      <list type="bullet" tight="true">
        <item>
          <paragraph>
            <text>3.1.1</text>
          </paragraph>
        </item>
        <item>
          <paragraph>
            <text>3.1.2</text>
          </paragraph>
          <list type="bullet" tight="true">
            <item>
              <paragraph>
                <text>3.1.2.1</text>
              </paragraph>
            </item>
            <item>
              <paragraph>
                <text>3.1.2.2</text>
              </paragraph>
            </item>
          </list>
        </item>
      </list>
    </item>
    <item>
      <paragraph>
        <text>4</text>
      </paragraph>
    </item>
  </list>

You need to add the width of the indentation of the parent to the width of its line marker to get the minimum indentation of the child. For 1, 2 and 4, the indentation is 0, but for 3, it is 1. The necessary indentation of cousins is irrelevant.