In this file: /packages/form-manager/process-procs.tcl

Change
   ad_util_set_variables $element name defaults
to
   ad_util_set_variables $element name defaults widget

And change
   if { [empty_string_p $value] } {
to
   if { [empty_string_p $value] || $widget == "none" } {


More details: http://dev.arsdigita.com/doc/templates/security.html