Purchase Receipts sometimes inherit "Additional Discount" from Purchase Order

Hello everyone

When “Additional Discount” is set on a Purchase Order, and one or more Purchase Receipts are made from that order, one of the following scenarios happens:
1- “Additional Discount” is set to zero on the Purchase Receipts.
2- For all Purchase Receipts, “Additional Discount” is set the same as its original value from the Purchase Order.
3- Some Purchase Receipts inherit the “Additional Discount” value, and some do not.

I couldn’t find a pattern in any of these scenarios, when does a Purchase Receipt inherit its Purchase Order’s “Additional Discount”?, and when does it not?

Thank you