mootools click event not working in iphone 6

Question

I'm using very simple markup button and attaching a click on it via mootools (latest 1.6):

<button id="btn">Click Me</button>
<script>
    window.addEvent('domready',function(){
        document.id('btn').addEvent('click',function(){
            //...do something
        });
     });
</script>

this code works everywhere except when i try to run it over iphone 6(i guess all mobile ios).

tried also to register touchstart event via mootools - with no luck. Anyone can point me to my mistake ? is it a mootools issue or ios issue ?