I created an automated action to copy a field from the related sales order to an invoice.  I only want it to copy the field value on creation so it can be modified on the invoice if desired.  The invoice is being created from the Create Invoice button on the Sales Order.  

The field does not copy to the invoice.  However, if I change the trigger to On Creation & Update it does work so I know my python script works.  It seems that the action that creates the invoice (Action ID: 544) does not appear to allow the On Creation to trigger.  The On Update will not work as it will trigger the action to run again on update and overwrite any changes to the field that might have been made on the invoice.

Can anyone shed any light on this.  Is this a bug or just how it works? If so are there any suggestions to work around it?

Can anyone shed any light on this. I'm using Studio so I don't have access to any of the methods or backend code to modify the flow of what is happening.