SERP May 2018 version
Does anyone know how to change this strange behaviour:

- create a Sales Order with an Item on it
- deliver and invoice it
- go back to the order, it's fine to make changes to any row not delivered/invoiced, such as adding a new row


BUT
- if you close the Order and go back in, any changes get the message: "Not allowed when order is delivered".

I'm not specially interested in why this is inconsistent, I'm more interested in finding out if there is a way to change Orders that have already been invoiced.