Eu uso contadores aninhados e escopo para criar uma lista ordenada:

<code>ol {
    counter-reset: item;
    padding-left: 10px;
}
li {
    display: block
}
li:before {
    content: counters(item, ".") " ";
    counter-increment: item
}</code>

<code><ol>
    <li>one</li>
    <li>two</li>
    <ol>
        <li>two.one</li>
        <li>two.two</li>
        <li>two.three</li>
    </ol>
    <li>three</li>
    <ol>
        <li>three.one</li>
        <li>three.two</li>
        <ol>
            <li>three.two.one</li>
            <li>three.two.two</li>
        </ol>
    </ol>
    <li>four</li>
</ol></code>

Espero o seguinte resultado:

<code>1. one
2. two
  2.1. two.one
  2.2. two.two
  2.3. two.three
3. three
  3.1 three.one
  3.2 three.two
    3.2.1 three.two.one
    3.2.2 three.two.two
4. four
</code>

Em vez disso, isso é o que eu vejo(numeração incorreta):

<code>1. one
2. two
  2.1. two.one
  2.2. two.two
  2.3. two.three
2.4 three <!-- this is where it goes wrong, when going back to the parent -->
  2.1 three.one
  2.2 three.two
    2.2.1 three.two.one
    2.2.2 three.two.two
2.3 four
</code>

Eu não tenho ideia, alguém vê onde está errado?

Aqui está um JSFiddle:http://jsfiddle.net/qGCUk/2/