Any idea why the system is not auto calculating the Q when we insert amount in Invoice lines matchin

Summary

User is inserting amount but the system is not auto calculating the quantity based on it

Content

User Receiving an invoice with amount = 16500 to match to PO line = 140000 and Quantity=1 

The user is inserting the amount in Invoice lines matching screen but the system is not calculating the Q based on it and keeping the whole quantity as its which is resulting in PO line close in some cases, if the user missed to change the quantity.

The user has to manually calculate the Quantity outside the system in order to have the correct quantity in this field

This is happening only when matching option = Order, where line quantity is defaulted