PreviewLostKeyboardFocus in WPF textbox called repeatedly in windows 8

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Windows

WPF

MessageBox

event

Hi please anybody knows reason for this just update here,

I've a TextBox control with PreviewLostKeyboardFocus.

Inside PreviewLostKeyboardFocus I'm calling a method to throw a custom MessageBox(System.Windows.Forms,MessageBox.Show())

So, when the message get called the PreviewLostKeyboardFocus calls itself again and again. I've put example code here,

private void txt1_PreviewLostKeyboardFocus_1(object sender, KeyboardFocusChangedEventArgs e)
        {
            try
            {
                txt1_call();
            }
            catch (Exception ex)
            {
                MessageBox.Show("Error : " + ex.Message);
            }
        }

 private void txt1_call()
        {
            try
            {
                System.Windows.Forms.MessageBox.Show("1");
                System.Windows.Forms.MessageBox.Show("2");
            }
            catch (Exception)
            {
                throw;
            }
        }

This looping not happening when I run the same code in windows7. But recently I've upgraded my machine to Windows8. In windows8 this problem arises. I'm using VS2012. I'm using framework 4.0. Anyway if I use System.Windows.MessageBox.Show() function its not looping. Anyway why for the first method worked in windows7 but not windows8? Suggestions welcome.