Since posting analysis in the comments is difficult, I declare this community wiki to be used for sharing our findings!

##Normal tag wiki:

    <div class="post-menu">
    
        <form class="form-submit" action="#" method="get">
            <input type="button" onclick="window.location.href='/edit-tag-wiki/702'"
                   value="Edit Tag Wiki">
        </form>
        
        <a href="/posts/196614/revisions">history</a>
        <span class="lsep">|</span>
        <a id="show-wiki-excerpt" href="#">show excerpt</a>
        <span class="lsep">|</span>
        <a href="/posts/196615/revisions">excerpt history</a>
        
    </div>

##pdf tag wiki:

    <div class="post-menu">
    
        <a href="/posts/247236/revisions">history</a>
        <span class="lsep">|</span>
        <a id="show-wiki-excerpt" href="#">show excerpt</a>
        <span class="lsep">|</span>
        <a href="/posts/247237/revisions">excerpt history</a>
        
    </div>

The markup for the `Edit Tag Wiki` button is completely missing and the `excerpt history` link ([http://superuser.com/posts/247237/revisions][1]) is broken.

When examining the [latest][2] history source, there is an **extra** newline at the end of the post (compared to the '[normal][3]' tag wiki above). Could this be causing the bug? Can someone with tag wiki edit privileges try replicating this on a different tag?

  [1]: http://superuser.com/posts/247237/revisions
  [2]: http://superuser.com/revisions/10cf01bb-fbf9-4a86-a6f9-3da2742fff00/view-source
  [3]: http://superuser.com/revisions/1d8b9383-b2aa-452e-ad95-7d141f5a7ced/view-source