DMD reports an error when trying to call the protected method of a superclass from inside the body of a delegate. Code to repro:

void layoutTransaction(void delegate() action) {
  action();
}

class Control {
  protected void onTextChanged() {}
}

class Label : Control {
  protected override void onTextChanged() {
    layoutTransaction({
      super.onTextChanged();
    });
  }
}

Output: class Control member onTextChanged is not accessible.

I think protected methods should be allowed to be called in this way. Note that private methods do seem to be accessible.