A couple of BC breaks occurred in the latest releases of Zend Framework (1.8.3/1.8.4) to Zend_Filter_Input. Specifically, the way "allowEmpty" and empty fields are being handled. Part of it is that isset() is being used on line 830 of Zend/Filter/Input.php, so null data values are considered missing, even though the key exists in the array. The usage of isset() should be changed to array_key_exists() on that line. This is a huge BC break as it now requires me to mark the presence of fields optional where I only previously had to allow them to be empty.