vue相关，为什么只有最后一个值改变了

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Vue 测试实例 - 菜鸟教程(runoob.com)</title>
<script src="https://cdn.staticfile.org/vue/2.4.2/vue.min.js"></script>
</head><body>

<div id="app">
    <c1 ref='ref1'></c1><hr>
    <c2></c2>
    <c2></c2>
</div>

<!-- js -->
<script>
    var cc=new Vue();
    var vm=new Vue({
        el:'#app',
        components:{
            c1:{
                template:"<input v-model='c1Val' @keyup='c1func'/>",
                methods:{
                    c1func:function(){
                        cc.$emit('ccfunc',this.c1Val);
                    }
                },
                data:function(){return {c1Val:0}}
            },
            c2:{
                template:"<h1>{{c2Val}}</h1>",
                data:function(){return {c2Val:1}},
                mounted:function(){
                    $this=this;
                    cc.$on('ccfunc',function(msg){
                        //$this.c2Val=msg;
                        $this.c2Val=vm.$refs.ref1.c1Val
                    })
                }
            }
        }
    })

如代码所示，修改c1的输入框，第二个c2回跟着改变，第一个c2始终不变。这是为什么

c2:{
        template:"<h1>{{c2Val}}</h1>",
        data:function(){return {c2Val:2}},
        mounted:function(){
                cc.$on('ccfunc', this.ccfunc)
        },
        methods: {
                ccfunc(msg){
                        $this=this;
                        $this.c2Val=msg;
                        console.log('haha', msg, vm.$refs.ref1.c1Val, $this.c2Val)
                        $this.c2Val=vm.$refs.ref1.c1Val
                }
        }
}