I am talking about the script handler configuration in LSWS console, not whether .php4 scripts are processed by PHP4 or PHP5. It is controlled by the "AddType" directives you mentioned.
You have to have a script handler defined for "php4", so LSWS will know that MIME type "application/x-httpd-php4" will be handled by that handler. And later on, you can change the handler using those "AddType" directives.
You should not remove the script handler configuration from the LSWS console.