Implementing Dynamic ToolTips: Preventing SetToolTip stack overflow

public partial class Form1 : Form
{
    Random rnd;
    ToolTip toolTip1;
    String[] tipText;

    public Form1()
    {
        InitializeComponent();
        InitializeToolTips();
        tipText = File.ReadAllLines(@"..\..\Form1.cs");
        rnd = new Random();
    }

    private void InitializeToolTips()
    {
        toolTip1 = new ToolTip();
        toolTip1.SetToolTip(button1, "Fixed text");
        toolTip1.SetToolTip(button2, "Variable text");
        button1.MouseHover += button_MouseHover;
    }

    private String NewTipText()
    {
        Int32 idx = rnd.Next(0, tipText.Length);
        return tipText[idx];
    }

    private void button_MouseHover(object sender, System.EventArgs e)
    {
        String proposed = NewTipText();
        if (!String.IsNullOrEmpty(proposed)) {
            toolTip1.SetToolTip((Control)sender, proposed);
        }
    }
}