angular 级联问题，重新选择的时候后面选项只清空一个

一个五级级联，重新选择的时候，为什么会出现如下情况？

代码如下：
一级类目





二级类目





三级类目





四级类目




五级类目

     .controller('searchController',['$scope',function($scope){
        $scope.address = [
            {
              "id":"1",
              "province":"服饰",
              "parent":"0"
            },       
            {
              "id":"1.1",
              "city":"女装/女士精品",
              "parent":"1"
            },        
            {
              "id":"1.1.1",
              "area":"裤子",
              "parent":"1.1"
            },        
            {
              "id":"1.1.1.1",
              "town":"休闲裤",
              "parent":"1.1.1"
            },        
            {
              "id":"1.1.1.1.1",
              "village":"加厚加绒休闲裤",
              "parent":"1.1.1.1"
            },       
            {
              "id":"1.2",
              "city":"男装",
              "parent":"1"
            },        
            {
              "id":"1.2.1",
              "area":"T恤",
              "parent":"1.2"
            },        
            {
              "id":"1.2.1.1",
              "town":"长袖T恤",
              "parent":"1.2.1"
            },        
            {
              "id":"1.2.1.1.1",
              "village":"韩版长袖T恤",
              "parent":"1.2.1.1"
            },
            {
              "id":"1.2.1.1.2",
              "village":"宽松版长袖T恤",
              "parent":"1.2.1.1"
            },
            {
              "id":"2",
              "province":"北京省",
              "parent":"0"
            },       
            {
              "id":"2.1",
              "city":"北京市",
              "parent":"2"
            },        
            {
              "id":"2.1.1",
              "area":"东城区",
              "parent":"2.1"
            },        
            {
              "id":"2.1.1.1",
              "town":"东东镇",
              "parent":"2.1.1"
            },        
            {
              "id":"2.1.1.1.1",
              "village":"东东村",
              "parent":"2.1.1.1"
            },       
            {
              "id":"2.2",
              "city":"xx市",
              "parent":"2"
            },        
            {
              "id":"2.2.1",
              "area":"xx区",
              "parent":"2.2"
            },        
            {
              "id":"2.2.1.1",
              "town":"xx镇",
              "parent":"2.2.1"
            },        

        ];
  }])

//类目过滤器
.filter('addressFilter',function () {
  return function (address,parent) {
    var filterAddress = [];
    angular.forEach(address,function(obj) {
      if(obj.parent === parent){
        filterAddress.push(obj);

      }
    });
    return filterAddress;       
  }
})

                <div ng-controller="searchController" style="margin-left: 50px;">
                    <select required="" ng-model="province" ng-options="item.id as item.province for item in address | filter:'0'" >
                        <option value="">一级类目</option>  
                    </select>  
                    <select  ng-model="city" ng-options="item.id as item.city for item in address | addressFilter:province" >  
                        <option value="">二级类目</option>  
                    </select>  
                    <select  ng-model="area" ng-options="item.id as item.area for item in address | addressFilter:city" >  
                        <option value="">三级类目</option>  
                    </select>    
                    <select  ng-model="town" ng-options="item.id as item.town for item in address | addressFilter:area" >  
                        <option value="" >四级类目</option>  
                    </select>
                    <select  ng-model="village" ng-options="item.id as item.village for item in address | addressFilter:town" >  
                        <option value="">五级类目</option>  
                    </select> 
                </div>