When a TwoWay dependency property is bound to a view model and the property is changed it tries to update the bound value in the viewmodel. If the viewmodel refuses to change and returns the same old value, the dependency property should not notify of any changes as it occurs in WPF.

For example:

<CheckBox x:Name="check" IsChecked="{Binding Selected}"/>

public class ItemData : INotifyPropertyChanged
{
    public ItemData() { selected = true; }

    private bool selected;
    public bool Selected
    {
        get { return selected; }
        set { // do nothing }
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

After setting check.IsChecked to False, the CheckBox should NOT raise the Unchecked and Checked events, and it should remain checked.