Here is a nice blog post describing the important differences between array_merge_recursive() and array_replace_recursive() functions in PHP. These are often overlooked when testing new developments with simpler data structures. Troubleshooting for it later is not too obvious.
RT @mamchenkov: PHP: array_merge_recursive() vs. array_replace_recursive() #WebDev #PHP #WebWork https://t.co/AKTTktWr9v