TwoWay Binding

I am evaluating the Syntax Editor for XML data.  I have the Syntax Editor control in my view bound to my viewmodel property and the data is loaded correctly, but changes are not pushed back to the viewmodel.

            <syntaxeditor:SyntaxEditor 
                Grid.Row="1"
                Text="{Binding Request, Mode=TwoWay}">
                <syntaxeditor:EditorDocument xml:space="preserve">
							<syntaxeditor:EditorDocument.Language>
								<syntaxeditor:XmlSyntaxLanguage />
							</syntaxeditor:EditorDocument.Language>
						</syntaxeditor:EditorDocument>
            </syntaxeditor:SyntaxEditor>

 The viewmodel property 

        private string request;
        public string Request
        {
            get { return request; }
            set
            {
                request = value;
                NotifyOfPropertyChange(() => Request);
            }
        }

 Is TwoWay binding not supported?