MetaClassImpl.getAttribute(Class,Object,String,boolean) drops super

class A {
  public x = 'A'
}
class B extends A {
  public x = 'B'
}

def a = new A()
println a.metaClass.getAttribute(A, a, 'x', false) // prints "A"

def b = new B()
println b.metaClass.getAttribute(B, b, 'x', false) // prints "B"

println b.metaClass.getAttribute(A, b, 'x', true) // prints "B", but "A" is expected
println ScriptBytecodeAdapter.getFieldOnSuper(A, b, 'x') // prints "B", but "A" is expected