Mangeto 1.9.3 - register and checkout issue

[BioL]

Currently I am testing my site checkout process. And I found out that with the option "register and checkout", after filling up email, password and placed order. The customer is not added after the order place.

Does anyone have any idea what is going wrong

Thanks

[cmubo]

This is a problem from supee 9767 involving the form key validation that was newly introduced
Here is a thread which answers your question:

https://magento.stackexchange.com/questions/177035/supee-9767-patch-ce-1-9-3-3-one-page-checkout-cus...

Here is the update log which outlines the problem: 
https://magento.com/security/patches/supee-9767