title: Search Result Source by ContentType causes zero results
body: <p>I am trying to build a SP 2013 Result Source that returns my specific content type.  Using the Build Tool I have this Query Text: </p>
  
  <pre><code>{searchTerms} ContentType:0x0120D520001F10DE640DA39D48A542F16414CE507B*
  </code></pre>
  
  <p>Which returns nothing.  I have run a full crawl and have items of that content type in my site.</p>
  
  <p>I noticed that when switching to the Test tab of the Build Your Query page the search query is modified somehow into this:</p>
  
  <pre><code>ContentType:0x0120D520001F10DE640DA39D48A542F16414CE507B* -ContentClass=urn:content-class:SPSPeople
  </code></pre>
  
  <p>I am not liking the addition of the -ContentClass as it appears may be messing things up a bit.  </p>
  
  <p>What must else I do to get this to return?</p>
  
  <p>Thanks</p>