Toolkit AutoCompleteBox tooltip issue for each listboxitem

Hi all,

I using AutoCompleteBox of Toolkit, with listbox inside a popup control.

Now, i binding a list to listbox. all good.. i using listbox.itemtemplate as:

<DataTemplate DataType="{x:Type types:StockBase}"><Grid><Grid.ColumnDefinitions><ColumnDefinition SharedSizeGroup="name" /></Grid.ColumnDefinitions><TextBlock 
                                                x:Name="txtName"
                                                Grid.Column="0" 
                                                TextAlignment="Left"
                                                Text="test"
                                                ToolTip="test123"/></Grid>                                     </DataTemplate>

but it seems that tooltip is not popsup? how to can i fix it?