title: md-select can't set selected value
body: <p>I have a <code>md-select</code> set up as follows:</p>
  
  <pre><code>&lt;md-select placeholder="Category" ng-model="current.Category" flex &gt;
      &lt;md-option ng-repeat="item in categories" ng-value="{{item}}"&gt;{{item.Name}}&lt;/md-option&gt;
  &lt;/md-select&gt;
  </code></pre>
  
  <p><code>@scope.categories</code> value is</p>
  
  <pre><code>[  
  {  
    "Name":"Commercial &amp; Industrial",
    "ParentId":null,
    "Categories":[  
       {  
          "Name":"Deceptive Marketing",
          "ParentId":19,
          "Categories":[  
  
          ],
          "Id":24,
          "ModifiedDate":"2015-08-06T07:49:53.0489545",
          "CreatedDate":"2015-08-06T15:49:51.707"
       },
       {  
          "Name":"Aggressive Agents",
          "ParentId":19,
          "Categories":[  
  
          ],
          "Id":25,
          "ModifiedDate":"2015-08-06T07:50:10.0026497",
          "CreatedDate":"2015-08-06T15:50:08.63"
       }
    ],
    "Id":19,
    "ModifiedDate":"08/06/2015 @ 7:49AM",
    "CreatedDate":"08/06/2015 @ 3:49PM"
   },
   {  
    "Name":"Competitive Supply",
    "ParentId":null,
    "Categories":[  
       {  
          "Name":"Security Deposit",
          "ParentId":20,
          "Categories":[  
  
          ],
          "Id":21,
          "ModifiedDate":"2015-08-06T07:49:30.3966895",
          "CreatedDate":"2015-08-06T15:49:25.8"
       },
       {  
          "Name":"Meter",
          "ParentId":20,
          "Categories":[  
  
          ],
          "Id":22,
          "ModifiedDate":"2015-08-06T07:49:34.6571155",
          "CreatedDate":"2015-08-06T15:49:33.3"
       },
       {  
          "Name":"Bill",
          "ParentId":20,
          "Categories":[  
  
          ],
          "Id":23,
          "ModifiedDate":"2015-08-06T07:49:41.7268224",
          "CreatedDate":"2015-08-06T15:49:40.357"
       }
    ],
    "Id":20,
    "ModifiedDate":"08/06/2015 @ 7:49AM",
    "CreatedDate":"08/06/2015 @ 3:49PM"
     }
  ]
  </code></pre>
  
  <p>The <code>md-select</code> works fine. But what I can't figure out is how to set select value. When I try setting the model <code>current.Category</code> to one of the values from the <code>$scope.categories</code> it doesn't get set. </p>