Can't classify linked source proposal as billed when create more than one sales order

Hi

I am not sure this is a issue or need to request the feature .
The situation is that there are two sales order that link one proposal . (That means there are two people work together . )
And i have enable the workflow function to auto classify source proposal as billed when create sales order .
When those sales order are created and the slaes order total amount is equal to proposal total amount , the source proposal won’t become billed .

But if that proposal just had one sales order , then it will become billed .

Are there any one could advice me this is a issue or need to request a new feature ?