Python Markdown attr_list syntax ignored by hyde

[jngeist]

As indicated in title, when I use the syntax described by the attr_list extension for Python Markdown, the attribute lists I designate are passed through, rather than rendered. So:

- This is a list item {: .testclass }

becomes

<li>This is a list item {: .testclass}</li>

rather than

<li class='testclass'>This is a list item.</li>

The relevant section is within a {% filter markdown|typogrify %} block in the template.

I've tried both specifying attr_list directly and as included in extra in my site.yaml, and neither has worked. The relevant section of my site.yaml:

markdown:
    extensions:
        - attr_list
        - meta
        - headerid
        - outline
        - toc

I'm not sure what's causing the problem, or where to go about debugging it. (The other markdown extensions I'm using work fine, including others loaded by extra when I've used it.) I've seen in another issue that @lakshmivyas uses attr_list without apparent issue, so it may just be me, but I can't figure this out.