DockingWindow.IsOpen not binding?

I'm using MVVM to add documents and tool windows to the docking & mdi framework and have all the properties I need working except the DockingWindow.IsOpen property binding. Is there a bug with binding to this property or maybe my code is incorrect?

View Bindings

<!-- docking:DockingWindow -->
<Style x:Key="DockingItemStyle" TargetType="docking:DockingWindow">
    <Setter Property="CanClose" Value="{Binding CanClose}"/>
    <Setter Property="CanMaximize" Value="{Binding CanMaximize}"/>
    <Setter Property="CanRaft" Value="{Binding CanRaft}"/>
    <Setter Property="Description" Value="{Binding Description}" />
    <Setter Property="HasTitleBar" Value="{Binding HasTitleBar}"/>
    <Setter Property="ImageSource" Value="{Binding ImageSource}" />
    <Setter Property="IsOpen" Value="{Binding IsOpen}"/>
    <Setter Property="IsSelected" Value="{Binding IsSelected}"/>
    <Setter Property="Title" Value="{Binding Title}"/>
    <Setter Property="CanDrag" Value="{Binding CanDrag}"/>
</Style>

 View Model

public abstract class DockingBase : INotifyPropertyChanged
    {
        private Boolean _CanClose = true;
        private Boolean _CanMaximize = true;
        private Boolean _CanRaft = true;
        private String _Description = String.Empty;
        private Boolean _HasTitleBar = true;
        private ImageSource _ImageSource;
        private Boolean _IsOpen = false;
        private Boolean _IsSelected = false;
        private String _Title = String.Empty;
        private Boolean _CanDrag = true;

        public DockingBase()
        {
            Id = Guid.NewGuid();
        }

        public Guid Id { get; protected set; }
        
        public Boolean CanDrag
        {
            get { return _CanDrag; }
            set
            {
                _CanDrag = value;
                NotifyPropertyChanged("CanDrag");
            }
        }
        
        public Boolean CanClose
        {
            get { return _CanClose; }
            set
            {
                _CanClose = value;
                NotifyPropertyChanged("CanClose");
            }
        }

        public Boolean CanMaximize
        {
            get { return _CanMaximize; }
            set
            {
                _CanMaximize = value;
                NotifyPropertyChanged("CanMaximize");
            }
        }

        public Boolean CanRaft
        {
            get { return _CanRaft; }
            set
            {
                _CanRaft = value;
                NotifyPropertyChanged("CanRaft");
            }
        }

        public String Description
        {
            get { return _Description; }
            set
            {
                _Description = value;
                NotifyPropertyChanged("Description");
            }
        }

        public Boolean HasTitleBar
        {
            get { return _HasTitleBar; }
            set
            {
                _HasTitleBar = value;
                NotifyPropertyChanged("HasTitleBar");
            }
        }

        public ImageSource ImageSource
        {
            get { return _ImageSource; }
            set
            {
                _ImageSource = value;
                NotifyPropertyChanged("ImageSource");
            }
        }

        public Boolean IsOpen
        {
            get { return _IsOpen; }
            set
            {
                _IsOpen = value;
                NotifyPropertyChanged("IsOpen");
            }
        }

        public Boolean IsSelected
        {
            get { return _IsSelected; }
            set
            {
                _IsSelected = value;
                NotifyPropertyChanged("IsSelected");
            }
        }

        public String Title
        {
            get { return _Title; }
            set
            {
                _Title = value;
                NotifyPropertyChanged("Title");
            }
        }

        protected void NotifyPropertyChanged(String property)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(property));
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
    }