As of 7.5.2, if there is a price change on an order line with no net accounting change, the system will create a Type 8 memo transactions with Far_Txn.COMMENTS set to describe the reason for the price change. In other words, if the price is being changed such that the base total is going negative and system is updating the base adjustment to avoid this, the system will create the Type 8 memo transaction.For example, let's say we have an invoiced membership order line where a 100% price reduction was made. The Type 4 is $120, and the Type 6 is -$120. Then, the membership end date is updated, which causes the order line amounts to be pro-rated, resulting in order line base unit price to be changed from $120 to $60, base adjustment to be changed from -$120 to -$60, and base total amount stays as $0, so there is no change in the transactions. This causes a situation where the order line amounts are not in sync with the Far_Txn amounts. This is fine from an accounting perspective, because AR and Revenue net to zero. However, from a data perspective the user has no clue about what happened and why the order line amounts are different than the txn amounts. Therefore, the system will create a Type 8 memo transaction for $0 to provide this information.
For more information on accounting transaction types, please see Accounting Transactions.