TextBox with validation loses ErrorTemplate on tab change

TabItem should be defined as follows:

<TabItem Header="Foo">
    <Border>
        <AdornerDecorator>
            <Grid>
                <TextBox Height="35" >
                    <TextBox.Text>
                         <Binding Path="pan_id" UpdateSourceTrigger="PropertyChanged">
                             <Binding.ValidationRules>
                                 <ps:PanIdValidation />
                             </Binding.ValidationRules>
                          </Binding>
                      </TextBox.Text>
                  </TextBox>
              </Grid>
          </AdornerDecorator>
      </Border>
  </TabItem>

The issue is, the Validation.Error cues are painted in the Adorner Layer. When you switch tabs, that layer is discarded.