There are 13 W3c validator errors in your HTML5.
I assume you are aware html5 is still in development and won't be released as "official" by the W3C for a few years yet. Consequently browser support for html5 currently varies greatly. But I don't think html5 is the main source of your problems here.
If you look through the html structural errors in your code you will see that it would fail even html4 validation. Fix the html errors and your problems should hopefully disappear.
When used correctly, <ol> works fine in IE9.