In order to add or edit recipes on a system with PHP 5.3, I had to disable AJAX by setting ajax_support=false in config_inc.php.
Otherwise the app complains about using the same ingredient multiple times - all ingredient id are 0 and refuses to create the recipe.
You fix it by adding the changing the "<?" tag to "<?php" for the following files:
modules\ingredients\get.php
modules\recipes\get.php