WPF Toolkit Combobox DisplayMemberPath not working

http://stackoverflow.com/questions/1105726/wpf-toolkit-combobox-displaymemberpath-not-working

OLD

<ContentPresenterx:Name="contentPresenter" 
                  Content="{TemplateBinding Content}" 
                ContentTemplate="{TemplateBinding ContentTemplate}" 
                  HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                  Margin="{TemplateBinding Padding}"/>

NEW

<ContentPresenterx:Name="contentPresenter" 
                  HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" 
                  Margin="{TemplateBinding Padding}"/>