How is the Self-ID Disability response value assigned for applicants with no response selected?

When a US applicant applies for a job, they have the option to complete the Self Identification of Disability form,  they have 3 options to select from:

Applicants are not required to provide a response and can click 'Next' to go to the next page.

I have noticed in my testing that if an applicant does not provide a response on this page but had previously provided one (for another application) then the old value is still present in the HR_APP_DIS record.DISABILITY_STS_USA field.  I expected that the default value would be 'X' - I Don't Wish to Answer if no response is provided, regardless of the response for prior applications.