this issue with PHP notices is something I have with a lot of workflows based on PHP, since I am a PHP developer myself I have set the error reporting in my php.ini to E_ALL | E_STRICT, meaning I will get all errors, warnings and notices printed. The quick fix is changing the setting in your php.ini file. The solution I've done is adding:
error_reporting(0);
to php-files in the workflows that are not working for me.