Zend_Soap_Client strips all options with a value of 0 from the options passed to other routines. Specifically: in file Soap/Client.php in the function getOptions() beginning at line 329: currently reads: if ($value == null) { unset($options[$key]); }

testing a value of zero against null using == returns TRUE, so this unsets all options with a valid value of zero. The specific option that brought this bug to my attention was cache_wsdl, which when set to WSDL_CACHE_NONE (0) failed to work.