动画<transition>包裹的元素设置ID选择器就不生效

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包裹的元素设置class选择器有效果但是改成id选择器就不生效是Vue的BUG吗

<!doctype html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        #main {
            width: 500px;
            height: 500px;
            border-radius: 50%;
            background-color: yellow;
            margin: 20px auto;
        }
        .v-enter,
        .v-leave-to {
            width: 10px;
            height: 10px;
            background-color: red;
            border-radius: 0;
        }
        .v-enter-active,
        .v-leave-active {
            transition: all 3s;
        }
    </style>
</head>
<body>
<div id="app">
    <button @click="show=!show">点我</button>
    <transition>
<!--        为啥用id动画就不生效呢????? class="main"就可以   -->
        <div id="main" v-show="show"></div>
    </transition>
</div>

<script src="lib/vue-2.4.0.js"></script>
<script>
    const app=new Vue({
        el:'#app',
        data:{
            show:false
        },
        methods:{
        }
    });
</script>
</body>
</html>`11