How Do You Associate Automatic Revenue Events to Multiple Draft Revenue Numbers Created during Same

I am working with a developer who is creating his first Project billing extension.  Everything was looking good until I started testing revenue adjustments based on splits and marking costs as non-billable for transactions that were originally revenue generated on the same draft revenue number.  I ran into a billing extension problem that I haven't encountered before.  Multiple events are being assigned to one draft revenue.  My test case was setup as follows: 

1.        Create a Project with Funding at the Top Task Level

2.        Add a Billing Assignment at the Top Task Level with an Amount and a Percentage

3.        Create several pre-approved expenditure batches against the project/task.