Unable to re-enter information to an uncompleted form

I am testing Membership Pro by entering details into the form fields that have already been set up. I have got a couple of friends to join our organisation and input their information into the fields created. One of the users abandoned the form, so it was not fully completed. He came back to it an hour or so later and started to re-enter his information.
This is where the problem occurred, the software will not let him fill in his 'Username' or 'Email address' as it is saying this is already being used by someone else. Therefor the form cannot be completed so that he can go to the Paypal payment part of the form at the end.
I have tried this myself and the same happens, it does not matter even if you clear your PC system Browsing History, cache, forms etc, the Pro software will still not let you complete the form.
It looks as thought the software somewhere is remembering the initial data input information. It would be helpful, if the form is abandoned halfway through, that the software clears the data from its memory, so that the user can start inputting the same information again and complete the membership form.
I hope this makes sense, please let me know if you need any further information.
Thank you.

Dear Surfer21,

Membership Pro is not part of Contact Enhanced and it's developed by another company.
I recommend you to contact it's developers in order to get it fixed.

Best regards,

I must apologise Douglas, sorry to have wasted your time.

No worries.

Have a blessed week.