I changed the file bug_report.php as following:

--- bug_report.php Wed Sep 15 14:27:24 2010
+++ bug_report.php Wed Sep 15 14:27:26 2010
@@ -103,10 +103,12 @@
foreach( $t_related_custom_field_ids as $t_id ) {
$t_def = custom_field_get_definition( $t_id );

• if (! $t_def['require_report'])
• continue;

• # Produce an error if the field is required but wasn't posted
  if ( !gpc_isset_custom_field( $t_id, $t_def['type'] ) &&

• ( $t_def['require_report'] ||
• $t_def['type'] == CUSTOM_FIELD_TYPE_ENUM ||

• ( $t_def['type'] == CUSTOM_FIELD_TYPE_ENUM ||
  $t_def['type'] == CUSTOM_FIELD_TYPE_LIST ||
  $t_def['type'] == CUSTOM_FIELD_TYPE_MULTILIST ||
  $t_def['type'] == CUSTOM_FIELD_TYPE_RADIO ) ) {
  @@ -141,7 +143,7 @@
  }

  $t_def = custom_field_get_definition( $t_id );

• if( !custom_field_set_value( $t_id, $t_bug_id, gpc_get_custom_field( "customfield$t_id", $t_def['type'], '' ), false ) ) {
• if( !custom_field_set_value( $t_id, $t_bug_id, gpc_get_custom_field( "customfield$t_id", $t_def['type'], $t_def['default_value'] ), false ) ) {
  error_parameters( lang_get_defaulted( custom_field_get_field( $t_id, 'name' ) ) );
  trigger_error( ERROR_CUSTOM_FIELD_INVALID_VALUE, ERROR );
  }

now only custom fields "Required On Report" are beeing checked and the default Values for those custom fields are used again.

something which realy bothers me is that the git-repository does not show those errors, but the actual 1.2.3 download did contain it!