Something very weird is happening on my P2 install after having tried this plugin.
I find myself unable to turn off markdown parsing!
What I did is: I tried both "Markdown on Save" and "Markdown for P2", to see which one worked better for me.
Then suddenly, I noticed that I could not see the raw markdown version anymore when editing. After hitting "publish", I would always see the full HTML, even in the edit window.
This worried me, so I disabled and deleted both extensions: this didn't help, any markdown is still auto-converted into html.
In addition to that, the syntax isn't transformed correctly.
# Something like this should give a H1 header
but it's transformed into:
<ol> <li>an ordered list</li> </ol>
So I'm not sure if the problem is directly related with your plugin, or with "Markdown on Save", but basically my usage of markdown is pretty much broken now :(