When you add a Batch assignment setting, there is a default batch assignment that uses a selection for all transactions. This cannot be removed. It will exist for all assignments for the same transaction type. (e.g., transaction type = Donations.) When you add another assignment to an assigment setting, you are effectivly fitting a smaller funnel into the larger one for All Transactions. However, the larger funnel continues to exist within that assignment stack. Thus, it is appropriate for all Donations to appear for all Assignment Settings for transactions of the same type.
We suggest creating only 1 batch assignment setting per transaction type, and adding as many batch assignments as desired to that assignment setting. Using multiple batch assignments for the same transaction type could create confusion for end users and is not advised.