nSM Forwarding between VM and dart2js disagree - VM loses default values

a.dart

void main() {
  var a = new AImpl();
  var b = new B(a);
  print("CALLING W/O NAMED ARG");
  b.a();
  print("CALLING W/ NAMED ARG");
  b.a(followLinks: false);
}

abstract class A {
  a({followLinks: true});
}

class AImpl implements A {
  a({followLinks: true}) {
    print('AImpl: followLinks is $followLinks');
    if (followLinks) print('yay');
    if (!followLinks) print('nay');
  }
}

class BestMixinEvar {
  final methods = <Symbol, Function>{};

  noSuchMethod(Invocation i) {
    var na = i.namedArguments;
    print('BestMixinEvar.noSuchMethod: namedargs: $na');
    if (i.memberName == #a) return Function.apply(methods[#a], [], na);
  }
}

class B extends A with BestMixinEvar {
  A delegate;

  B(this.delegate) {
    methods.addAll(<Symbol, Function>{
      #a: delegate.a,
    });
  }
}