I think what you going to have to do here is use the GotFocus event and manuall open the dropdown.  Something like this:

 <ig:XamComboEditor ItemsSource="{Binding}"
                    DisplayMemberPath="Name"
                    OpenDropDownOnTyping="True"
                    CustomValueEnteredAction="Add"
                    GotFocus="XamComboEditor_GotFocus"  />

private void XamComboEditor_GotFocus(object sender, RoutedEventArgs e)
{
    ((Infragistics.Controls.Editors.XamComboEditor)sender).IsDropDownOpen = true;
}

This will pop open the dropdown as soon as the control gets focus, even if the user has not typed anything.

Devin 

Hi gmcalab,

when you click on drop down arrow of editable XamComboEditor the list opens and you can type text in TextBox to filter the list.

Hope that helps.

Best regards,
Milena Mitova
Software Engineer in Test I
NetAdvantage for Silverlight LoB