Version

2.5.13

Reproduction link

NG pattern (functional)
https://codesandbox.io/s/004vv2onw0

OK pattern (no functional)
https://codesandbox.io/s/q9k5q8qq56

Steps to reproduce

I found can't use components option when functional single file component.

<template functional>
  <div>
    <some-children />
  </div>
</template>

<script>
import SomeChildren from "./SomeChildren"

export default {
  components: {
    SomeChildren
  }
}
</script>

It's occure Unknown custom element.

What is expected?

Not occure Unknown custom element and use child component

What is actually happening?

It's occure Unknown custom element

In workaround, it not occure when use Vue.component.

import Vue from "vue"
import SomeChildren from "./SomeChildren"
Vue.component("some-children", SomeChildren);

export default {}

// can use  <some-children />