Using TwoWay mode in AutoCompleteTextBox

Hello,

I've following xaml code in my WPF app.If I keep he Mode for "Text" as TwoWay, the autocomplete text box does not respond to mouse clicks...i.e.lets say i  type  'A' in the searchbox, then it does show all the values starting with A, but when I select any item in the dropdownlist, my product details pane does not get populated.

If I change the mode to OneWayToSource, then everything works fine as expected.What am i missing here please?

Thanks.

XAML code:

 <wpf:AutoCompleteTextBox VerticalAlignment="Top"                                     
                                     Margin="1,0"
                                     DisplayMember="Name"
                                     Text="{Binding Path=ProductName, Mode=TwoWay}"
                                     Watermark="Search"
                                     IconPlacement="Left"
                                     IconVisibility="Visible"
                                     Provider="{Binding SuggestionProvider}"
                                     SelectedItem="{Binding Path=SelectedProductName, Mode=TwoWay}" 
                                     x:Name="MySearchBox" TabIndex="0">

ViewModel:

 public string ProductName
        {
            get
            {
                return m_ProductName;
            }
            set
            {
                m_ProductName = value;
                OnPropertyChanged("ProductName");
            }
        }