RMA Created without discount line

Dear  peers,

We have an issue where an RMA order is created on one of the lines from the original sales order, As part of Business Operations,

Now The Issue here is the discount created in the original sales order is not copied to the RMA and this is causing a big problem for us and we are unable to understand the same .

I want to know what is the issue causing this , the impact of the issue is there is  mismatch between the original invoice and the RMA invoice .

Please let us know what is the Root Cause for this, and also please let us know what can be done to avoid this cases.