When entering a new payment or a new automatic payment plan, the amount of the payment is not being distributed correctly to student siblings based on the business rule to distribute proportionally based on balance using the overall balance. The program is looking at the amount for Open Charges/Refunds/Advance Deposits amount on each record rather than the Overall Balance on the record. This is resulting in students with a $0 or credit balance who have unapplied activity being included in the distribution of the payment or payment plan.
Download and install the latest patch, which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.