I think this is a bug. Can you create an issue. A temporary work around is to define the CRUD methods again in ConcreteQuestion. Maybe something like:
create: function(...) {..},
parseModel: function(...) {...}
}
var CRUD = {
create: function(...) {..},
parseModel: function(...) {...}
}
var QuestionModel = can.Model. extend(CRUD,{});
var ConcreteQuestion = can.Model.extend(CRUD,{});