This error message is caused by a Magento 1.x bug that has always been there (at least up to current 1.9.3.1 version), but few gave it attention or observed it.
I explained it in detail here: http://stackoverflow.com/a/41490292/1470684
Mihai MATEI
Software Engineer
Hello, thank you for your post. Could you please tell me how to solve this? Regards Rundi