stable and es6 code version produce different output

@MaBe/@Gordon, did not notice that a() was defined as 'classical'/regular function but b() was defined as arrow function. That was by the way the reason that I did not change the TMQ regular - constructor - function in tinyMQTT to an arrow function, but everything else I did convert. I was first even concerned to change the prototype functions into arrow functions... but since they do not use this there is no problem...