Possible bug: Changing the country of an address gives the error "The identification number is incorrect or has already been used."

[30knees]

A customer accidentally entered their address with Germany as the country. I want to edit the address so the country is now Spain. Upon clicking save, I get the error: "The identification number is incorrect or has already been used." However, I can edit the address if I keep Germany as the country. 

UPDATE: I just wanted to create a totally new address for the customer but got the same error. So I added a . to the DNI field and I could suddenly change the country in the original, saved address. So this has something to do with the DNI (which was left empty)?

Edited August 3, 2023 by 30knees