Comment 7 for bug 98437

There are files in both Zope2 and Zope3 that produce this bug.

http://svn.zope.org/Zope/trunk/lib/python/Testing/ZopeTestCase/zopedoctest/functional.py?view=auto
http://svn.zope.org/zope.app.testing/trunk/src/zope/app/testing/functional.py?view=auto

As noted, the problem isn't in testbrowser. As a workaround, you can open the testbrowser in some URL that won't be affected by the broken HTTP_REFERER value and then use browser.getLink to navigate from there to the URL you need to test provided, of course, that a link is available on the page initially loaded.