~$ perl ./mech-test.pl
Before freeze & save: Set-Cookie: PHPSESSID=p9ogedv2qf1r5h664la79is1j2; path=/

Page session id: p9ogedv2qf1r5h664la79is1j2 

~$ perl ./mech-test.pl
After thaw & submit: Set-Cookie: PHPSESSID=tq3devkvch2t5fsq6qbp707de4; path=/

Page session id: tq3devkvch2t5fsq6qbp707de4