Workaround for invalid Media Query minification (WebGrease and System.Web.Optimization)

gistfile1.cs

  public class BundleConfig
    {
        public static void RegisterBundles(BundleCollection bundles)
        {
            var siteCssBundle = new StyleBundle("~/css/site").IncludeDirectory("~/public/css", "*.css");
            siteCssBundle.Transforms.Clear();
            siteCssBundle.Transforms.Add(new CustomCssMinify());
            bundles.Add(siteCssBundle);
        }
    }

    public class CustomCssMinify : CssMinify
    {
        public override void Process(BundleContext context, BundleResponse response)
        {
            // Workaround for a bug in WebGrease/System.Web.Optimization
            // missing leading whitespace before 'and', 'not', 'only'
            // hopefully a fix will come!
            base.Process(context, response);
              response.Content = response.Content
                .Replace(")and ", ") and ")
                .Replace(")not ", ") not ")
                .Replace(")only ", ") only ");
        }
    }

I would assume that this is only called once when changes are detected?