title: As soon I add "props" to the component I get: Error in callback for watcher "function () { return this._data.$$state }"
body: <p>I get a very strange error which I can't locate.</p>
  
  <blockquote>
    <p>[Vue warn]: Error in callback for watcher "function () { return this._data.$$state }": "Error: [vuex] do not mutate vuex store state outside mutation handlers."</p>
  </blockquote>
  
  <p>I am using vuex in strict mode. Despite the error I am not mutating any vuex store state outside mutation handlers. The component is not using vuex at all. I created a test component that does not use anything like below.</p>
  
  <pre><code>&lt;template&gt;
    &lt;div&gt;
      TEST COMPONENT
    &lt;/div&gt;
  &lt;/template&gt;  
  &lt;script&gt;
  export default {
    name: 'testComponent',
    props: ['testProp'],
  }
  &lt;/script&gt;
  </code></pre>
  
  <p>As soon I add the props part I get the error. I am not able to represent the whole project here or reproduce it. But there is nothing special anyway. </p>