为什么序列化对象不能存储在const常量中

<?php
    const FOOBAR = "Foo"; // Works.
    const FOOBAR = array("Foo", "Bar"); // Doesn't work.  Makes sense.
    const FOOBAR = serialize(array("Foo", "Bar")); // Doesn't work.  Okay.  :'
    define("FOOBAR", serialize(array("Foo", "Bar"))); // Works!  The heck?
 ?>

PHP Parse error: syntax error, unexpected '(', expecting ',' or ';'

为什么常数可以被设置为序列化对象，当他们用define()声明，而不是用const关键字?我遗漏了什么?

(用5.3.5-1ubuntu7.2测试)