I Overloaded as follows on wp8-xaml and I have no issues?
EDIT: Actually it seems to randomly crash sometimes, I'll try to resolve this with MS as it doesn't seem to be cocos2d-x thats causing it its the interop of c++ and c#.
This way It will react the exact same way as android when we overload the virtual void keyBackClicked(void) function in our layers
Don't forget to add setKeypadEnabled(true); in the init of your layers.
That may have been the cause of your issue?