c# - Enter button in AutoCompleteTextBox not working -

i'm using autocompletetextbox textbox(from on here: https://wpfautocomplete.codeplex.com/) in c#/wpf app. code per below.when hit "enter" or "tab" button after typing text in textbox,i dont see selectedproductname getting set. advise missing here please?

thanks.

xaml:

<wpf:autocompletetextbox verticalalignment="top"                                       height="25"                                      width="320"                                      margin="1,0"                                      displaymember="name"                                      text="{binding path=productname, mode=onewaytosource}"                                      watermark="search"                                      iconplacement="left"                                      iconvisibility="visible"                                      provider="{binding suggestionprovider}"                                      selecteditem="{binding path=selectedproductname, mode=twoway, updatesourcetrigger=propertychanged}"                                      x:name="actb" tabindex="0" > 

viewmodel:

public productnameviewmodel selectedproductname         {                         {                 return m_selectedproductname;             }             set             { //invoke method on wcf service product details             }         }