In WP's trac this is what I get:
<div id="ctxtnav" class="nav">\n <h2>Ticket Navigation</h2>\n <ul>\n <li class="first">\n <a href="/ticket/2499" title="Ticket #2499">Previous Ticket</a>\n </li>\n <li class="first last">\n\n <a href="/ticket/2501" title="Ticket #2501">Next Ticket</a>\n </li>\n </ul>\n</div>
In Edgewall's trac:
<div id="ctxtnav" class="nav">\n <h2>Ticket Navigation</h2>\n\n</div>
You might want to check in the keyword "ctxtnav" and see where the include is going wrong. I'd think this has to be a feature, to enabled navigation or not.