I have a custom field in sales order that is sourcing from the customer record. The problem I am running into is that if the field in the Customer record is blank and the user put's text in the sales order field when the record is opened again that field is blank. I assume this is because the field is still trying to source. Is there a way around this via the UI?

I encounter this when the Store Value box is not checked on the Custom Field. It depends on your use case if this needs to be checked or not. I guess you need to check since you want to allow users to override?

I ended up using a workflow to populate the field but only on create.