CheckBox DataBinding Doesn't Update

Hello,

I am databinding a Boolean property to a checkbox. I am doing the databind in a TwoWay mode so I expect that when the checkbox is checked for the property to change to true, and when it is unchecked it should change to false.

This works when checking the checkbox (the property changes to true) but doesn't work when unchecking the checkbox (the property stays set to true).

Does anybody know why this is?

Here is my Xaml:

<DataTemplate x:Name="PlayerList"><CheckBox Content="{Binding name}" IsChecked="{Binding isSelected, Mode=TwoWay}" /></DataTemplate><StackPanel><ListBox x:Name="Players" ItemsSource="{Binding listOfPlayers}" ItemTemplate="{StaticResource PlayerList}"/></StackPanel>

My ViewModel:

private ObservableCollection<Players> _listOfPlayers;
   public ObservableCollection<Players> listOfPlayers
      {
         get { return _listOfPlayers; }
         set
           {
              _listOfPlayers = value;
              onPropertyChanged("listOfPlayers");
           }
      }

and my model:

private bool _isSelected;


public bool isSelected
   {
      get
         {
            return _isSelected;
         }
      set
         {
            if (_isSelected != value)
               {
                  _isSelected = value;
                  onPropertyChanged("isSelected");
               }
         }
    }