User Defined Values not auto refreshing

We have a UDF on Sales Order - called "Customer Remarks". This field needs to auto-populate with the contents of the "Notes" field relating to the business partner that is added to the order. I have attached an image of the Values setup and the code in the query.

If users hit Shift+f2, the field fills correctly, but does not automatically when Customer/Vendor Code changes. I have tried 'Customer/Vendor name' field as well.Can anyone suggest how i can get this to work automatically?

SELECT T0.[Notes] FROM OCRD T0 WHERE T0.[CardCode]  = $[$4.0.0]