troester, here's one big issue - I'm managing this site for an organization that is not very organized. Several months ago someone took over management of this database. During that time, I performed the standard Joomla updates (a few weeks after release) and then any Fabrik updates that were available. I did not realize this form was broken until a new person from the organization took back over this week. So, I have no idea which update broke the form.
I checked on the protostar template and the form is still broken on the frontend. I don't think it's another plugin or issue (though I'm not sure) because there's really nothing going on in this site except Community Builder user list and Fabrik tables that connect to it. VERY basic.
Hugh - here's the information I could find (I'm not sure what helps you, but I'd be happy to give backend access):
.../components/com_fabrik/controllers/form.php:154
153 || in_array($input->get('format'), array('raw', 'csv', 'pdf')))
154 || in_array($input->get('format'), array('raw', 'csv', 'pdf'))
.../plugins/system/redirect/redirect.php:112
KExceptionHandlerAbstract->_handleException()
exception ParseError#a72a
PlgSystemRedirect::doErrorHandling()
.../plugins/system/redirect/redirect.php:91