Im trying to bind 2 different WPF controls to the same property in the ViewModel, a CheckBox.IsChecked and an Expander.IsExpanded. The behavior I want to achieve is to have the CheckBox affect the ViewModel (and therefore the Expander as well), but not the other way bound.
Something like:

```
Checkbox Checked -> ViewModel property set to frue -> Expander.Expand
Checkbox Unchecked -> ViewModel property set to false -> Expander.Collapse
Expander Expanded -> Nothing else affected
Expander Collapsed -> Nothing else affected

```

Here's the XAML:

```
<Window x:Class="WpfApplication9.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Expander IsExpanded="{Binding IsChecked, Mode=OneWay}">
        <Expander.Header>
            <CheckBox IsChecked="{Binding IsChecked}" Content="Is Checked"/>
        </Expander.Header>
        <TextBlock Text="Expanded!"/>
    </Expander>
</Window>

```

and the Code:

```
using System.ComponentModel;
using System.Windows;

namespace WpfApplication9
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            DataContext = new ViewModel();
        }
    }

    public class ViewModel: INotifyPropertyChanged
    {
        private bool _isChecked;
        public bool IsChecked
        {
            get { return _isChecked; }
            set
            {
                _isChecked = value;
                NotifyPropertyChange("IsChecked");
            }
        }

        protected void NotifyPropertyChange(string PropertyName)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(PropertyName));
        }

        public event PropertyChangedEventHandler PropertyChanged = delegate { };
    }
}

```

Now my problem is, as soon as I click on the Expander to expand / collapse it, the Binding seems to stop working. Can anyone explain to me why this is happening and how do I achieve this? Thanks in advance!