Possible Vue bug

HTML

<script src="https://unpkg.com/moment"></script>
<script src="https://unpkg.com/vue@2.4.2"></script>
<div id="test">
<test :myarray="[1,2,3]"></test>

</div>


<template id="arraybug">
  <div  >
<span v-for="i in myarray">{{i}},</span>

<button v-on:click="add()">
click
</button>
{{mycomputed}}
</div>
</template>

JavaScript

Vue.component('test', {
 props:['myarray'],
  template:'#arraybug',
  methods:{
  	add:function(){
    	alert(this.myarray);
      this.myarray.push(1);
  	}
  },
  computed:{
  	mycomputed: function(){
    	return this.myarray.length;
    }
  }
 });

var test = new Vue({
  el:"#test"});