User starts paypal transaction, backs out. no payments processed till timeout.

Hi there, Ive noticed something now that ive deployed my usermanager based pay as you go hotspot to the wild.

If a user creates a user in the signup page, and then proceeds to go to the paypal payment screen, and then backs out or doesnt finish. The user-manager will no longer process payments (accept IPN notifications) for any new signup until the payment times out.

It seems user manager does not accept paypal payments in parallel. Is there any way to fix this behavior? Can I adjust the payment timeout value somehow? had to refund 3 payments yesterday because of this.