Form Element "Type: File" Problem

I created a form using FB. One of the fields is to be an optional field for attaching a document. However, even though I unchecked the Required check-box (it is checked by default) when I selected this form element, it still shows the red asterisk next to the field label. After I uploaded the form to my website to test it, it won't let me submit the form until I do attached a file. Therefore, it acts like it is a required field. Additionally and not surprisingly, there is no validation error message displayed either if I haven't attached a file. FYI, the validation does work properly for the fields where I do want this capability. It's just the file type where I have a problem.

BTW, I encounter the same problem even when I start with an empty page and add just this file type form element to the form.

Any advice on how to correct this situation would be greatly appreciated. Thanks in advance.