Starting from PHP 5.3.9 there is a brand new php.ini option: max_input_vars. For further information have a look here:
The default value is 1000. Due to this restriction it can happen, that your Page Creator can’t hold more than 20 boxes at the same time. We recommend to increase this value if you are planing to build up large scale websites with lots of boxes. Keep in mind, that inside a box you can also make use of short codes.
Link with more further information’s: http://anothersysadmin.wordpress.com/2012/02/16/php-5-3-max_input_vars-and-big-forms/