<h3 dir="auto">Version</h3>
<p dir="auto">2.3.0</p>
<h3 dir="auto">Reproduction link</h3>
<p dir="auto"><a href="https://jsfiddle.net/superboy2k/50wL7mdz/38665/" rel="nofollow">https://jsfiddle.net/superboy2k/50wL7mdz/38665/</a></p>
<h3 dir="auto">Steps to reproduce</h3>
<p dir="auto">Click Init, Click Update a few times, click Add =&gt; see the error  in the console</p>
<h3 dir="auto">What is expected?</h3>
<p dir="auto">to update the ui correctly</p>
<h3 dir="auto">What is actually happening?</h3>
<p dir="auto">TypeError: Cannot read property 'key' of undefined<br>
at sameVnode (unpkg.com/vue@2.3.3:4769)<br>
at updateChildren (unpkg.com/vue@2.3.3:5128)<br>
at patchVnode (unpkg.com/vue@2.3.3:5180)<br>
at updateChildren (unpkg.com/vue@2.3.3:5096)<br>
at patchVnode (unpkg.com/vue@2.3.3:5180)<br>
at updateChildren (unpkg.com/vue@2.3.3:5096)<br>
at patchVnode (unpkg.com/vue@2.3.3:5180)<br>
at Vue$3.patch [as <strong>patch</strong>] (unpkg.com/vue@2.3.3:5305)<br>
at Vue$3.Vue._update (unpkg.com/vue@2.3.3:2327)<br>
at Vue$3.updateComponent (unpkg.com/vue@2.3.3:2443)</p>
<h3 dir="auto">Vue.js version</h3>
<p dir="auto">2.0.0-rc5</p>
<h3 dir="auto">Reproduction Link</h3>

<p dir="auto"><a href="https://jsfiddle.net/oldpig/zb4zLxkb/1/" rel="nofollow">https://jsfiddle.net/oldpig/zb4zLxkb/1/</a></p>
<h3 dir="auto">Steps to reproduce</h3>
<p dir="auto">Click any tab to switch</p>
<h3 dir="auto">What is Expected?</h3>
<p dir="auto">Tab switched, everything goes fine.</p>
<h3 dir="auto">What is actually happening?</h3>
<p dir="auto">There are warnings in console, multiple times each switch.</p>
<p dir="auto">I am aware that this warning is introduced in rc.5. But I am not sure what goes wrong.</p>