Why is textbox format firing validators?

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ASP.NET

C#3.5

I have a web form that has eight textboxes and eight rangevalidators on it. When a user enters their data the numbers are formatted on textbox text change with commas. Here is the format code I am using:

TextBox1.Text = string.Format("{0:0,0}", double.Parse(TextBox1.Text));

The format works fine until the user clicks on submit and four out of eight validators fire. What could have caused the firing of the validators and how can I fix it?

protected void TextBox1_TextChanged(object sender, EventArgs e)
    {
        RangeValidator1.Validate();
        TextBox1.Text = string.Format("{0:0,0}", Int32.Parse(TextBox1.Text));
        TextBox2.Focus();
    }