* since we don't name fields CoreField-Subject (and doing so
  would mean magic frobbing of request_args before Create)
  share the meaning of what a CoreField is with a library function

html/FormTools/Field

@@ -12,7 +12,8 @@ my $queue      = $m->notes('queue');
 my $field_type = 'custom';
 my $field_label ||= $label;
 my $cf;
-if ( $name =~ /^(Requestors|Cc|AdminCc|Subject)$/i ) {
+
+if ( RT::Extension::FormTools::is_core_field($name) ) {
     $field_type = 'core';
     my $res = $m->notes(
         core_fields_on_page => [ @{$m->notes('core_fields_on_page')||[]}, $name ] );

html/FormTools/Form

@@ -17,7 +17,7 @@ foreach my $key (keys %request_args) {
 }
 
 foreach my $key (keys %request_args) {
-   next unless ($key =~ /CoreField-(\d+)/ );
+   next unless RT::Extension::FormTools::is_core_field($key);
    my $field = $1;
    delete $request_args{$key} if ($core_fields{$field});
 }

lib/RT/Extension/FormTools.pm

@@ -3,4 +3,22 @@ use strict;
 
 package RT::Extension::FormTools;
 
+our $VERSION = '0.03';
+
+=head2 is_core_field
+
+passed one argument (field name) and checks if
+that is a field that we consider 'core' to
+RT (subject, AdminCc, etc) rather than something
+which should be treated as a Custom Field.
+
+Naming a Custom Field Subject would cause
+serious pain with FormTools
+
+=cut
+
+sub is_core_field {
+   return $_[0] =~ /^(Requestors|Cc|AdminCc|Subject)$/;
+}
+
 1;