Cannot edit contribution created by authorize.net recurring contribution

When editing a contribution that was created as a authorize.net recurring contribution, you will get the error:

The sum of fee amount and net amount must be equal to total amount

The Contribution code enforces this rule only when the fee amount, net amount and total amount are all not empty.

However, the authorize.net recurring contribution code will insert a default fee amount and net amount of "0.00" - which is not empty.

There's a forum post here on the topic:

http://forum.civicrm.org/index.php/topic,31948.0.html