[Vue 2.0]named slot disappear

[carrytao]

Vue.js version

2.0.0-beta.7

Reproduction Link

http://jsbin.com/walejonumi/1/edit?html,js,output

Steps to reproduce

focus the input

What is Expected?

The before slot should not disappear

What is actually happening?

The before slot disappears

If you switch to Vue 1.x, it works fine.
I use render function later and find that in the first render, this.$slots.before and this.$slots.default all exist, but when re-rendered, this.$slots.before is undefined, and all the slot come into this.$slots.default

[carrytao]

Find another question in the demo. When this.focus change, the wrapClass updated, but the class on the dom doesn't update.