RnD explains that this has been a deliberate decision to exclude PR lines created from DOP in the RFQ flow. And the main reason being, that new functionalities needed to be implemented that will keep track of the connection to the DOP order all the way through the RFQ flow. When RnD implemented the RFQ functionality, there was no time to consider all possible sources for the demand, and hence they had to exclude Requisitions Lines with demand from DOP. 

If we create a Request for Quotation we can send the Quotation to multiple Supplier and each Supplier may have different Lead Time for the Part. The Orig. Due Date in DOP Order screen is calculated based on the Lead time, but if there is a different lead time for different Supplier, system can not record it. For this reason Requisition to Request unction is not available for PR created from DOP.

They have deliberately restricted this quotation flow as they want to back calculate the lead times and come up with some estimated date figures at the DOP Header release. If the users are allowed to use the quotation flow, we can’t be certain with these lead times and hence do the above calculation in a real time business scenario. 

As per RnD there have been very valid requests about this by customers over the years and has added this request to the Supply Chain product backlog to cater this requirement in future releases but there is no information yet when it will be implemented.