Validation.HasError does not trigger again if new error comes in while already true

I use MVVM and my object implement IDataErrorInfo. When a property is set, I run custom validation methods and if the validation passes, I return String.empty, which sets Validation.HasError to false. If the validation fails, Validation.HasError is set to true. I have a style that I use for "required controls" (controls that will perform the validation) and set's the ToolTip of the control to whatever the error is like this:

<Style x:Key="RequiredControl" TargetType="{x:Type Control}" >
    <Style.Triggers>
        <Trigger Property="Validation.HasError" Value="true">
            <Setter Property="ToolTip" Value="{Binding (Validation.Errors), Converter={StaticResource ErrorConverter}, RelativeSource={x:Static RelativeSource.Self}}"/>
        </Trigger>
    </Style.Triggers>
</Style>

And the ErrorConverter:

public class ZynErrorContentConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var errors = value as ReadOnlyObservableCollection<ValidationError>;
        if (errors == null) return "";

        return errors.Count > 0 ? errors[0].ErrorContent : "";
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

The problem is this: The user enters something invalid...and the Validation.HasError is set to true. The tooltip updates as it is supposed to. If the user attempts to correct the error, but enters a value that causes a different type of invalidation, the tooltip should show the new error string, but this doesn't happen. The error shows as the same error from the first error. I know why this happens (I think)...Because the Trigger is not triggered because the Validation.HasError never changes from True -> False -> True.

Does anyone have any experience with this or some advice as to how to force the trigger?

This appears to be the answer: IDataErrorInfo With Multiple Error Messages for a Property

Basically, you bind to the current item and use a ContentPresenter to display the error. It worked for my code.