Line type Tax code default validation ignored at the time of Order Booking in R12

Hello Team,

We recently upgraded instance from 11.5.10.2 to 12.1.3

In 11i we get error : 'Please specify the tax code. The line type requires tax calculation' when we try to book sales order and if the line has no tax classification code.Hence it doesnt allow to book. But in R12 it allows to book. I would like to know reason and how can we implement same validation in R12.

Issue reprodction Steps in upgraded R12 instance.

1. Log on to any OM Responsbility

2. Create an Order with specfic order type(Standard- which has tax code enabled for the transaciton type) . Selcte the header deatils.