I tried changing the  

  <Popup x:Name="PART_Popup"

part of both 

  <ControlTemplate x:Key="ComboEditor_EditableComboBoxTemplate" TargetType="{x:Type ComboBox}">

and

  <ControlTemplate x:Key="ComboEditor_NonEditableComboBoxTemplate" TargetType="{x:Type ComboBox}">

but my chages are ignored.

Any help will be appriciated.

Thank you.