JS截断后台存储过程

前台的asp:GridView模版组里加入了这样一个button
<asp:Button ID="button1" runat="server" Text="删除" OnClick="button1_Click" onClientClick="return confirm('确实要删除吗?')"/>
调试正常,但当点击确定后,后台操作完全被忽略,存储过程没有被执行,而是直接跳到response.write一行,下面是代码:
 try
                {
                    connection.Open();
                    cmd.ExecuteNonQuery();
                    Response.Write("<script language='javascript'>alert('操作成功！');window.location.href='UserManager.aspx';</script>");
                                        
                }====
改用后台强制后效果一样(为方便找到按钮控件,已将ID改为btn_del)
   protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.DataRow)
         {
             Button btnDelete = (Button)e.Row.FindControl("btn_del");
             btnDelete.Attributes.Add("OnClick", "return confirm('确实要删除吗?')");
         }
         
    }请教达人!!!!