Exit during checkout: Registration remains pending.

Dear all,

I have come across this problem:

Day A:

• A user fills out the registration form
  • Registration is saved and set to pending.
• Completes billing form
• the summary is presented
• User exists, due to reasons.

Day B
The user returns and reruns this process.

Expected result:

• A user fills out the registration form
  • Registration is saved and set to pending.
• Completes billing form
• the summary is presented
• User completes payment
  • Registration is saved and set to complete.

Actual result:

• A user fills out the registration form
  • Registration is denied. Because of the registration of Day A.

How can I fix this?