The breadcrumb navigation in the admin documentation templates uses absolute references, rather than relative ones. This means that it won't work if you have your admin server running from anything other than the "root" directory.
Example:
My admin server is running at http://example.com:8000/admin/
But the code for the breadcrumb looks like this:
<div class="breadcrumbs">
<a href="/">Home</a> ›
<a href="/doc/">Documentation</a> ›
<a href="/doc/models/">Models</a> › {{ name }}
</div>
Which means that the link for documentation (e.g.) will go to http://example.com:8000/doc/, instead of http://example.com:8000/admin/doc.
The links need to be changed to use the relative style links of the other page templates. e.g.,
<div class="breadcrumbs">
<a href="../../../">Home</a> ›
<a href="../../">Documentation</a> ›
<a href="../">Models</a> › {{ name }}
</div>
The affected files are in django/conf/admin_templates/doc