I was having a similar problem. I solved it by adding a type attribute to the ol tags:
<ol type="1st level">
<li>One</li>
<ol type="2nd level">
<li>1.1</li>
<li>1.2</li>
</ol>
<li>Two</li>
<ol type="2nd level">
<li>2.1</li>
<li>2.2</li>
</ol>
<li>Three</li>
<li>Four</li>
<li>Five</li>
</ol>
Esmi’s code above works for me, too, though. I hadn’t thought to enclose the 2nd level ol tags within the 1st level li tags.