This is a very old post. In fact, the filter that I posted 3 years ago will not actually do anything and never would have.
In order to have ACF return default values when a field has never been saved to the DB you must use the field key. This is the case with any action or filter for any field that has never been saved.
All ACF functions really operate on the field key. When you use the field name ACF must look up the field key in the DB. If that field has never been save/updated ACF cannot find the field key. Without the field key ACF cannot get field settings for the field.
