The report was added some time ago and when it was added, there was a user request to be able to see whether or not a payment had been when the invoice was created.
We have three options:
1. Remove the payment information.
2. Include posted payments.
3. Leave the report as it currently exists.
Any of the three options is valid with the third being the only one that ensures that we are not removing or altering functionality that a user currently relies upon.
I will put a check mark on option two for you and we will see what other users vote for.