DBD::mysql mysql_insertid returns 0

dbd-mysql-mysql_insertid.pl

## version
# Perl 5.18.1
# DBI 1.636
# DBD::mysql 4.033

## create table SQL
# create table t(id integer not null auto_increment, primary key (id)) ;

## this can get mysql_insertid
my $dbh = DBI->connect("dbi:mysql:test;user=root");
my $sth = $dbh->prepare("insert into t() values()");
$sth->execute();
print $dbh->{mysql_insertid}

## use ping method before getting mysql_isnertid, mysql_insertid returns 0
my $dbh = DBI->connect("dbi:mysql:test;user=root");
my $sth = $dbh->prepare("insert into t() values()");
$sth->execute();
$dbh->ping;
print $dbh->{mysql_insertid}