Consider the following:

class C {
  boolean b
  boolean isB() { }
}
class D extends C {
  void test() {
    super.b // MissingMethodException: No signature of method: bugs.C.getB() is applicable for argument types: () values: []
  }
}

As noted in GROOVY-1736 and GROOVY-6097 the property expression "super.b" is converted to "super.getB()" during classgen. The class C does not have a generated getB() method because there is an explicit isB() method.