In the UK at least (I assume it's very similar in the US because our (current) laws on it are based on theirs in regards to this stuff AFAIK), if a parent with care goes on to state benefits, and the state is therefore providing for the child, as well as the parent with care, the childs part of that benefit should in part, be recouped by the non-resident parent, the PWC gets no choice in the matter.
In that regard this has probably followed the letter of the law.
The intent of the law however... to see a child monetarily (when unfortunately not possible to be fully) supported by two parents probably doesn't cover two parents and a unofficial donor.