keyup.enter: problem with select enter

HTML

<script src="//unpkg.com/vue/dist/vue.js"></script>
<script src="//unpkg.com/[email protected]/lib/index.js"></script>

<div id="app">
  <el-form :model="form" :rules="rules" ref="form" label-width="100px">

    <el-form-item label="Product" prop="productId">
      <el-select v-model="form.productId" filterable @change="handleProductChange(form.productId)">
        <el-option label="Zone one" value="shanghai"></el-option>
        <el-option label="Zone two" value="beijing"></el-option>
      </el-select>
    </el-form-item>

    <el-form-item label="Qty" prop="qty">
      <el-input v-model="form.qty" ref="qty" @keyup.enter.native="onSubmit('form')"></el-input>
    </el-form-item>

    <el-form-item label="Price" prop="price">
      <el-input v-model="form.price" ref="price"></el-input>
    </el-form-item>

    <el-form-item>
      <el-button type="primary" @click="onSubmit('form')">Query</el-button>
    </el-form-item>
  </el-form>
</div>

SCSS

@import url("//unpkg.com/[email protected]/lib/theme-default/index.css");

Babel + JSX

var Main = {
    data() {
      return {
        form: {
          productId: '',
          qty: '',
					price:''
        },
				rules: {
                    productId: [
                        {required: true}
                    ],
                    qty: [
                        {required: true},
                        {type: 'number', message: 'Paid amount must be a number'}
                    ],
                    price: [
                        {required: true},
                        {type: 'number', message: 'Paid amount must be a number'}
                    ],
                }
      }
    },
    methods: {
      onSubmit(formName) {
        console.log('submit!');
				this.$refs[formName].validate((valid) => {
                    if (valid) {
                       alert('submited');
                    } else {
                        return false;
                    }
                });
      },
			handleProductChange(val){
                console.log('change', val);
                setTimeout(()=>{
                            this.$refs.qty.$el.querySelector('input').focus();
                        },500);
                //this.$refs.qty.$el.querySelector('input').focus();
            },
    }
  }
var Ctor = Vue.extend(Main)
new Ctor().$mount('#app')