<p dir="auto">Hello,</p>
<p dir="auto">I try to upgrade my vue app to 1.0 and get the following error over 200 times for each for loop:<br>
<code class="notranslate">[Vue warn]: Duplicate value found in v-for="book in books": "\"". Use track-by="$index" if you are expecting duplicate values.</code></p>
<p dir="auto">This is my template code with 2 loops:</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="&lt;select name=&quot;relation[books][]&quot; multiple=&quot;&quot; tabindex=&quot;-1&quot; style=&quot;display:none;&quot;&gt;
        &lt;template v-for=&quot;book in books&quot;&gt;
            &lt;option :value=&quot;book.id&quot; selected&gt;
                {{book.title}}
            &lt;/option&gt;
        &lt;/template&gt;
    &lt;/select&gt;

    &lt;div id=&quot;sortable-books&quot; class=&quot;extended-relation-select__list --entries&quot;&gt;
        &lt;template v-for=&quot;book in books&quot;&gt;
            &lt;div&gt;
                &lt;i class=&quot;fa fa-bars&quot;&gt;&lt;/i&gt;

                {{book.title}}

                &lt;div class=&quot;pull-right&quot;&gt;
                &lt;span class=&quot;buttons&quot;&gt;
                    &lt;i class=&quot;fa fa-times&quot; @click=&quot;removeEntry($index)&quot;&gt;&lt;/i&gt;
                &lt;/span&gt;
                &lt;/div&gt;
            &lt;/div&gt;
        &lt;/template&gt;
    &lt;/div&gt;"><pre class="notranslate"><code class="notranslate">&lt;select name="relation[books][]" multiple="" tabindex="-1" style="display:none;"&gt;
        &lt;template v-for="book in books"&gt;
            &lt;option :value="book.id" selected&gt;
                {{book.title}}
            &lt;/option&gt;
        &lt;/template&gt;
    &lt;/select&gt;

    &lt;div id="sortable-books" class="extended-relation-select__list --entries"&gt;
        &lt;template v-for="book in books"&gt;
            &lt;div&gt;
                &lt;i class="fa fa-bars"&gt;&lt;/i&gt;

                {{book.title}}

                &lt;div class="pull-right"&gt;
                &lt;span class="buttons"&gt;
                    &lt;i class="fa fa-times" @click="removeEntry($index)"&gt;&lt;/i&gt;
                &lt;/span&gt;
                &lt;/div&gt;
            &lt;/div&gt;
        &lt;/template&gt;
    &lt;/div&gt;
</code></pre></div>
<p dir="auto">And this is my array with the entries:</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="&quot;books&quot;: [
    {
      &quot;id&quot;: &quot;55&quot;,
      &quot;title&quot;: &quot;Wir nennen es Politik&quot;
    },
    {
      &quot;id&quot;: &quot;1&quot;,
      &quot;title&quot;: &quot;Die Bienen&quot;
    },
    {
      &quot;id&quot;: &quot;2&quot;,
      &quot;title&quot;: &quot;Finnisches Feuer&quot;
    },
    {
      &quot;id&quot;: &quot;3&quot;,
      &quot;title&quot;: &quot;Träume Digitaler Schläfer&quot;
    }
  ]"><pre class="notranslate"><code class="notranslate">"books": [
    {
      "id": "55",
      "title": "Wir nennen es Politik"
    },
    {
      "id": "1",
      "title": "Die Bienen"
    },
    {
      "id": "2",
      "title": "Finnisches Feuer"
    },
    {
      "id": "3",
      "title": "Träume Digitaler Schläfer"
    }
  ]
</code></pre></div>
<p dir="auto">Can someone explain me the issue here?</p>
<h3 dir="auto">Version</h3>
<p dir="auto">2.5.2</p>
<h3 dir="auto">Reproduction link</h3>
<p dir="auto"><a href="https://codepen.io/spenspazmer/pen/aLXGGY?editors=1011" rel="nofollow">https://codepen.io/spenspazmer/pen/aLXGGY?editors=1011</a></p>
<h3 dir="auto">Steps to reproduce</h3>
<p dir="auto">1.Create a v-for list with items<br>
2.Inspect and observe the item elements<br>
3.Trigger an action that shifts and pops the list<br>
4.Observe</p>
<h3 dir="auto">What is expected?</h3>
<p dir="auto">The items should be removed without re-rendering the item list.</p>
<h3 dir="auto">What is actually happening?</h3>
<p dir="auto">The whole list is re-rendered.</p>
<hr>
<p dir="auto">Adding new elements works just as expected, just as triggering several pop or shift operations, doing a single list splice from the end or start. Performing a splice from the beginning and the end respectively triggers the same re-rendering problem.</p>