net amount sometimes incorrect for events involving partial payments.

See attached image.

(One set of) Steps to recreate ( there could be others):

1. Sumit an online 'pay later' registration for an event.
2. Edit the event and make a partial payment toward the event fee.
3. Repeat 2 as often as needed until the event fee is fully paid.

Result: The FINAL partial payment amount is (incorrectly) added to the net amount, leading to the situation where net amount > total amount.