I am storing User object in Zend_Auth_Storage_Session as a array element on valid authentication.
$authSession = new Zend_Auth_Storage_Session();
$authSession->write(array('user' => $user));
When I read Zend_Auth_Storage_Session, users lastLogin property, which is DateTime instance on session write, is string.
cbaby, Am not saying this is the solution but its working fine for me because I can access the ‘lastLogin’ normally. Maybe something else wrong somewhere. Ensure that your setting the date correctly.