PHP markdown in "Textile compatibility mode"... how?

[eluser]minimal design[/eluser]
I'm moving a bunch of textile formated post to a CI CMS I'm building and I want to use markdown instead of Textile.

I included the PHP markdown file as a helper and it work great. PHP markdown is supposed to have a Textile compatibility mode (described towards the top of that page). I tried to get it working as described but nothing happens. The markdown is still converted successfully but the textile stuff remains as plain text.

I'm wondering if anyone's got this compatibility mode working, and if so, how they set it up.

Thanks!