If we did change the server behavior, it seems unlikely that every driver would adjust their behavior to the new server behavior all at once and that they would all get it right while also all preserving backward compatibility with current releases in case a newer driver is used with an older server. I don't think that's likely. What would probably happen is that many drivers would ignore the change, leaving applications to cope with the differences between server versions, and some would change the driver behavior categorically, breaking compatibility with older server versions, and some would make mistakes in implementing support for the new behavior. And maybe we would also find that the new behavior isn't ideal for everybody any more than the current behavior is ideal for everybody.
To test how the driver would currently react if the server did respond with an error I made a small change