Why is a new line created when I change a quantity?

OP purchase order

Next status is 400, ready to match when we decide to change the quantity

Change Qty from "1" to "2" ..... it seems like the change is accepted... when you review the order again it has written a new line.

Also, info from the original line does not get copied to the new line.

I don't see any knowledge docs about this; I don't see anything in the manual about this; I don't see any proc options about this.

It isn't a huge deal but it does look a bit confusing.

We are on 9.1