User Registration

I am having an issue with a registration form on a website.

Example:

The first name and last name fields are marked as required in the code and every time I try to submit the form without the firstname/lastnmae missing, I get an error stating the fields are required.

On a couple of user accounts, someone has been able to get registered without having the firstname/lastname being filled out.

Any idea on what I can do to verify that it is actually working correctly?

I have tried to break the form but every time the site functions as expected and makes me fill out the entire form.

Anyone have any suggestions?

Thanks for your assistance!