c# 把内容写入文件问题

下面代码写入文件为什么后面会多出几行代码。c#文件
rotected void Button1_Click1(object sender, EventArgs e)
    {
        FileStream fs = new FileStream(Server.MapPath("htmlTemplate/1方法.htm"), FileMode.Open, FileAccess.Read);
        StreamReader m_streamReader = new StreamReader(fs, Encoding.GetEncoding("utf-8"));
        m_streamReader.BaseStream.Seek(0, SeekOrigin.Begin);
        this.txtContext.Text = "";
        string strLine = m_streamReader.ReadLine();
        while (strLine != null)
        {
            this.txtContext.Text += strLine;
            strLine = m_streamReader.ReadLine();
        }
        m_streamReader.Close();    }
    protected void Button2_Click1(object sender, EventArgs e)
    {
        FileStream fs = new FileStream(Server.MapPath("htmlTemplate/1方法.htm"), FileMode.OpenOrCreate, FileAccess.Write);
        StreamWriter m_streamWriter = new StreamWriter(fs, Encoding.GetEncoding("utf-8"));
        m_streamWriter.BaseStream.Seek(0, SeekOrigin.Begin);
        m_streamWriter.WriteLine(txtContext.Text);
        m_streamWriter.Flush();
        m_streamWriter.Close();
    }html模版
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>
</head>
<body>
    <table id="tableTemp" class="tableTemp" cellpadding="2px" cellspacing="0" style="border-collapse: collapse"
        border="1px" bordercolor="#CCCCCC">
        <tbody>
            <tr>
                <th>
                    计划1
                </th>
                <th>
                    计划2
                </th>
                <th>
                    计划3
                </th>
                <th>
                    计划4
                </th>
            </tr>
            <tr>
                <td>
                    <input class="input" type="text">
                </td>
                <td>
                    <input class="input" type="text">
                </td>
                <td>
                    <input class="input" type="text">
                </td>
                <td>
                    <input class="input" type="text">
                </td>
            </tr>
        </tbody>
    </table>
</body>
</html>