Don't use a hashref ({...}) if you have multiple identical keys  (for this purpose, the API also allows an arrayref).

my $hashref = {DATA=>"foo", DATA=>"bar", VALUE=>"Submit"};

use Data::Dumper;
print Dumper $hashref;

__END__
$VAR1 = {
          'VALUE' => 'Submit',
          'DATA' => 'bar'         # where's 'foo'?
        };
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(not saying this will necessarily fix the hang, but it's wrong anyway)

See also LWP::Debug.