I am not sure whether I am able to provide answer to this psychosis-problem, but there is a very good discussion on this (in German) in the Wörterbuch der Individualpsychologie (Dictionary of Individual Psychology), by Brunner & Titze. Ansbacher & Ansbacher discuss this shortly in their The Individual Psychology of Alfred Adler. Acording to them, the neurotic understands social interest (this is based on a quotation by AA), but the psychotic has lost his/her grip of this idea more or less completely (see pp. 302-303). So the difference is a difference of degree, but it is still a huge difference, in my mind.