Even with a cleaner code like that. the problem still persist...

I fogot to mention you have to insert some text in textbox between each clic to repoduce the problem (one of the textbox must have the focus when you clic on the button

public partial class Page : UserControl
    {
        DispatcherTimer _timer = new DispatcherTimer();

        public Page()
        {
            InitializeComponent();

            _timer.Interval = new TimeSpan(0, 0, 1);
            _timer.Tick += new EventHandler(_timer_Tick);
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            this.IsEnabled = false;
            _timer.Start();
        }

        void _timer_Tick(object sender, EventArgs e)
        {
            this.IsEnabled = true;
            ((DispatcherTimer)sender).Stop();
        }
    }