Change event is not called when checked value changed using ref

I was trying to create a select all feature. Following is my component,

(function(){
    var template = ' <table>\
                        <tr>\
                            <td rowspan=2><input type="checkbox" @change="allSelectChanged"/>All</td>\
                        </tr>\
                        <tr v-for="i in rows">\
                            <td  ><input type="checkbox" ref="select" @change="changedSelection(i,$event)" />Selection </td>\
                        </tr>\
                    </table>';
    var component = { 
        template : template,
        data:function(){
            return {
                rows:5
            }
        },
        methods:{
            allSelectChanged:function(e){
                _.each(this.$refs.select,function(s){
                    s.checked = e.target.checked;
                });
            },
            changedSelection:function(i,e){
                console.log("Selection changed",i,e.target.checked);
            }
        }
    }
    Vue.component('sample', component);
})();

When I checked/unchecked any checbox changedSelection function is called. But when I checked/unchecked all checkbox, all the other check boxes are getting selected but changedSelection function is not getting called.

Why changedSelection is not called when the change is made through ref??