serialize() works on internal classes. It doesn't work on virtual properties and this problem usually occurs with internal classes.

What you want is more control over serialization. Eventually the solution is a set of new magic callbacks 
function /* string */ __serialize()
static function /* instance */ __unserialize(string $data)

__serialze() would need to return the string used to recreate the instance and __unserialize() would recreate it from the passed string. We could also make __unserialize() a non static fucntion in which case the instance would be created prior to calling the function. However the static functionality allows much more flexibility. 

For example the static functionality allows instance creation through factory methods and they could store the information needed to reread a xml document or reopen a database connection.

Closing as serialization for internal classes is already supported if the class implements it.