Changing widgets with Allowed Values Intact

If I first set a CCK Text field to the "Autocomplete for allowed values list" widget and specify an Allowed Values List - Save - and then change the widget to "Autocomplete for existing field data" the field still reads from the allowed value list and rejects unlisted values.

Solution: revert to "Autocomplete for allowed values list", remove Allowed Values, Save and change widget back.

Honestly, I like that it reads the allowed values list, if only it would still accept new values. That said, I've seen that functionality marked Won't Fix in other issues.