CAM::PDF reload DV node

Question

Have a node with default values like this:

bless({
  gennum => 0,
  objnum => "281",
  type   => "object",
  value  => bless({
              gennum => 0,
              objnum => 281,
              type   => "dictionary",
              value  => {
                          DV      => {
                                       gennum => 0,
                                       objnum => 281,
                                       type   => "string",
                                       value  => "some default val",
                                     },

trying to replace value by

if ( my $on = $doc->getFormField( $_ ) ){
   $on->{value}->{value}->{DV}->{value} = "New default value";
 } $doc->getFormFieldList();

but the result is the same default value. Where is a problem? Seems like a cache of hash of cam::pdf fields