When I use secure_form http://pylonshq.com/docs/en/0.9.7/thirdparty/webhelpers/html/html/#webhelpers-html-secure-form and @authenticate_form tandem formencode htmlfill clear (set to "") _authentication_token field. This happen when I send form with wrong values. This problem was appeared after I upgrade python eggs related with Pylons 0.9.7 framework.
Snippets of code