What logic restricts multiple Legal Entities on Order apart from the flag "error"?

Summary: Purchase order should not have multiple legal entities on purchase order lines. Apart from the "error" flag for the attribute "Multiple Legal Entities on Order" in "Configure Requisitioning Business function" what else overrides this functionality?

Content (please ensure you mask any confidential information):

After setting up the attribute "Multiple Legal Entities on Order" to "Error" it should create two separate purchase orders from Process Requisitions task and should not allow to combine two Requisitions and create one Purchase order.

Tested case:

1. Created one Requisition with BPA and another requisition with no supplier details (Both having different Legal Entities)
2. Selected both Requisitions on "Process Requisitions" task and added to document builder instead of showing error it allowed to create the Purchase Order and after submitting Purchase Order went for approval. (It should have raised an error)