<h3 dir="auto">Version</h3>
<p dir="auto">2.5.17</p>
<h3 dir="auto">Reproduction link</h3>
<p dir="auto"><a href="https://codesandbox.io/s/zwm20ozlym" rel="nofollow">https://codesandbox.io/s/zwm20ozlym</a></p>
<h3 dir="auto">Steps to reproduce</h3>
<p dir="auto">check reproduction url</p>
<h3 dir="auto">What is expected?</h3>
<p dir="auto">Duplicate keys detected to be warned</p>
<h3 dir="auto">What is actually happening?</h3>
<p dir="auto">Duplicate keys detected not warned</p>
<hr>
<p dir="auto">when addVnodes is called, vnodes with same key are not warned</p>
<p dir="auto">When a class is set in an dom element which is being initied with Vue and the same class is set in the component root dom element, the final result is a double class. You can see the results <a href="https://jsfiddle.net/miljan/8z2phjsx/1/" rel="nofollow">here</a>, check with the console the dom and you should see "compClass compClass" instead of just one.</p>
<p dir="auto">It's not a big deal but doesn't seem the expected behaviour.</p>