title: ValidationRule Red Border Issue
body: <p>In my WPF Application, I have created ValidationRules for my TextBoxes so that it will not allow an empty string which works fine and shows a red border with text telling the user it can not be empty. When the application launches, all the fields are blank waiting for input but I still see the red border around them. Is this normal behavior? Note: I would prefer it firing after either a propertychange event or lostfocus event fires when the user using the form not when the form initially loads.</p>
  
  <p>Example of the validation I am doing:</p>
  
  <pre><code> &lt;TextBox x:Name="itemNum" HorizontalAlignment="Left" Height="23" Margin="82,58,0,0"     VerticalAlignment="Top" Width="90"
              HorizontalContentAlignment="Left" VerticalContentAlignment="Center" PreviewKeyDown="ItemNum_PreviewKeyDown" 
              PreviewTextInput="ItemNum_PreviewTextInput" TabIndex="0" Validation.ErrorTemplate="{StaticResource validationErrorTemplate}"&gt;
              &lt;TextBox.Text&gt;
                  &lt;Binding Path="rxID" Mode="TwoWay" StringFormat="{}{0:#}" UpdateSourceTrigger="PropertyChanged"&gt;
                      &lt;Binding.ValidationRules&gt;
                          &lt;MY:TextBoxNotEmptyValidationRule x:Name="rxIDValidation" ValidatesOnTargetUpdated="True" /&gt;
                      &lt;/Binding.ValidationRules&gt;
                  &lt;/Binding&gt;
              &lt;/TextBox.Text&gt;
          &lt;/TextBox&gt;
  </code></pre>
  
  <p>My TextBoxNotEmptyValidationRule Class:</p></p>
  
  <pre><code>public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
       {
          string str = value as string;
          if (string.IsNullOrEmpty(str))
          {
              return new ValidationResult(false, "Value CAN NOT BE empty");
          }
          return ValidationResult.ValidResult;
      }
  </code></pre>