This is worrisome. Vague advanced directives may be overturned but specific ones should NOT be.
In my opinion, no one, and I mean NO ONE, has the right to keep me alive past the point at which I want it done, as long as I've clearly specified my wishes in writing ahead of time. If it's against Gods wishes that I opt out of this earth, then I'll find out when I'm dead. It's between Him and me, not anyone else.
LQ