Attempting to pay a doubled lineitem billing results in MULTIPLE_PAYMENTS_FOR_XACT error

Evergreen Version 2.6.3. and 2.7.5

This bug is in relation to Bug 1261835

If the staff member does not know how to clear the doubled lineitem billing (caused by checking materials in via the Items Out tab within the patron's account - to clear the double billing, click Refresh within the patron account before attempting to pay the fine) or doesn't notice the event has occurred and attempts to pay the fine, the staff member will see either a "No payment or patron credit applied" message or a MULTIPLE_PAYMENTS_FOR_XACT error.

From my testing, it looks like, the act of selecting or deselecting lineitems determines the message staff receive. I cannot nail down the exact event that occurs to receive one message versus the other.

During my initial testing, any lineitem selected that is still recognized as Checked Out, staff will see the No payment or patron credit applied message.

When the Checked Out lineitem is deselected and an attempt to make a payment is made, staff will see the MULTIPLE_PAYMENTS_FOR_XACT error.

During another test, all materials were checked in. Selecting multiple lineitems resulted in the No payment or patron credit applied message. Selecting only one lineitem resulted in the MULTIPLE_PAYMENTS_FOR_XACT error.

Attached is a screencast of the first example, where one of the items was still checked out. Again, this isn't the only scenario tested that caused this behavior. The patron in this screencast is fake, and I am using a training staff client.