title: set operation on a property return IList is not working
body: <p>I have an interface with:</p>
  
  <pre><code>IList&lt;int&gt; CategoryIDs {get;set;}
  </code></pre>
  
  <p>Then a class that inherits this interface:</p>
  
  <pre><code>public IList&lt;int&gt; CategoryIDs
  {
  
       get {}  // this part works
       set { _categoryIDs = value;   // error!
  
  }
  </code></pre>
  
  <p>The set part of the accessor reports an error:</p>
  
  <blockquote>
    <p>cannot implicity convert type <code>IList&lt;int&gt;</code> to <code>List&lt;int&gt;</code>.</p>
  </blockquote>
  
  <p>What should I do? confused.</p>