Angular Material virtual repeat, select checkbox changes more than one item

I'm working on Angular (version 1.4.9) Material virtual repeat deferred loading and slightly modified the example code.

When I select one checkbox in the list, a second one is selected. I don't know how to solve this behaviour. But I think it has something to do with the repeated rows of the list. Any ideas how to fix that?

html code:

...
<div class="virtualRepeat">
<md-virtual-repeat-container id="vertical-container">
  <md-list>
    <md-list-item md-virtual-repeat="item in listCtrl.teaData" md-on-demand class="md-2-line" flex>
      <md-checkbox md-no-ink class="md-primary" ng-click="emptyFunction()" ng-model="item.active" aria-label="select"></md-checkbox>
      <div class="md-list-item-text">
        Name: {{item.name}}
        ID: {{item.id}}
      </div>
    </md-list-item>
  </md-list>
</md-virtual-repeat-container>
</div>
...

Code from the controller creating the list:

...
var vm = this;

var ListItems = function() {
  this.count = 0;
  this.pageSize = 15;
  this.loadedPages = {};
  this.listData = [];
  this.getTeaCount_();
}

ListItems.prototype.getItemAtIndex = function(index) {
  var currentPage = Math.floor(index / this.pageSize);
  var page = this.loadedPages[currentPage];
  if (page) {
    return this.listData[index];
  } else if (page !== null) {
    this.getPage_(currentPage);
  }
}

ListItems.prototype.getLength = function() {
  return this.count;
}

ListItems.prototype.getPage_ = function(currentPage) {
  this.loadedPages[currentPage] = null; 
  this.loadedPages[currentPage] = [];

  var pageOffset = currentPage * this.pageSize;

  for (var i = pageOffset; i < pageOffset + this.pageSize; i++) {
    this.loadedPages[currentPage].push(i);
  }

  RestFactory.fetchCurrentPage(currentPage).then(angular.bind(this, function(tea) {
    for(var i = 0; i < tea.items.length; i++) {
      this.listData.push({
        name: tea.items[i].name,
        id: tea.items[i].id
      });
    }
  }));

}

ListItems.prototype.getTeaCount_ = function() {
  RestFactory.fetchCount().then(angular.bind(this, function(count) {
    this.count = count;
  }));
}

vm.teaData = new ListItems();