You must set “Save Custom” to yes.
What happens when you have it set the way you do.
ACF gets the choices allowed by the field. These are the only choices that will be shown every time. ACF then gets the value for the current field. If the field allows custom values and the value is not one of the values added by the field then ACF adds it to the choices.
Without saving custom values to the field ACF has no way to determine what other values should be listed. It only has the choices set by the field and the current value of the field to work with.
