Don't know ...
Now you can add custom values with
Shift+Enter Add the contents of the current Tag Panel field to the list of custom list values for that field.
See also the documentation.
That was not possible before.
Also, it was not possible to add custom values to any other field - which is now.
The procedure is now the same for all tag panel fields.
Anyway - until it gets changed again, you would have to cope with the current method.
And that has been true for the last couple of years: