Keypress Event Form problem

Hello guys. I created an Windows Forms Application template, and on my Form I attached a Label. I activated the KeyPress event for my Form, and when I press any key ( letter, number ), it adds that key to the label1. But when I attached a button on my Form, and I open the application and I press any key, nothing happens. Follow my screenshots please:
- my simple form before to press any Key: http://img211.imageshack.us/img211/1312/firstform.png
- my simple form after I press 5 keys (h,e,l,l,o): http://img14.imageshack.us/img14/2299/2ndform.png
- my simple form with a button on it: http://img32.imageshack.us/img32/9040/buttonadded.png

And here is the code source:

using System;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_KeyPress(object sender, KeyPressEventArgs e)
        {
            label1.Text += e.KeyChar;
        }
    }
}