Required Field Validator not working on controls inside dynamically generated user control

I have a user control containing few server controls like text boxes and drop down lists.

i have also added few required field validation controls. Normally these validation work fine, if I add the user control in design time.

But when I add the user control dynamically, the validation control just don’t work and page is posted back. 

User Control:

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="myUserControl.ascx.cs" Inherits="myUserControl" %><table cellpadding="0" cellspacing="0" ><tr><td><asp:TextBox runat="server" ID="txtLastName" Width="80px" MaxLength="64" /><asp:RequiredFieldValidator ID="RequiredFieldValidator1" ControlToValidate="txtLastName" runat="server" ErrorMessage="Required Value" Display="None"></asp:RequiredFieldValidator><ajaxToolkit:ValidatorCalloutExtender ID="ValidatorCalloutExtender1" runat="server" TargetControlID="RequiredFieldValidator1"></ajaxToolkit:ValidatorCalloutExtender></td><td><asp:TextBox runat="server" ID="txtFirstName" Width="80px" MaxLength="64" /><asp:RequiredFieldValidator ID="RequiredFieldValidator2" ControlToValidate="txtFirstName" runat="server" ErrorMessage="Required Value" Display="None"></asp:RequiredFieldValidator><ajaxToolkit:ValidatorCalloutExtender ID="ValidatorCalloutExtender2" runat="server" TargetControlID="RequiredFieldValidator2"></ajaxToolkit:ValidatorCalloutExtender></td><td><asp:Button ID="btnDelete" runat="server" Text="Delete" OnClick="DeleteButton_Click" CausesValidation="false" /></td></tr></table>

Containing Form Markup:

<form id="form1" runat="server"><div><div align="right" ><asp:Button ID="btnAdd" runat="server" Text="Add Order Line" onclick="btnAdd_Click" CausesValidation="false" /></div><asp:PlaceHolder runat="server" ID="DynamicNameList" /><asp:Button ID="btnSubmit" runat="server" Text="Submit" onclick="btnSubmit_Click" /></div></form>

Containing Form Code:

 public partial class WebForm1 : System.Web.UI.Page, IDynamicControlContainer
        {
            protected void Page_Load(object sender, EventArgs e)
            {
                foreach (string id in LoadControlIdList())
                {
                    Create(id);
                }
            }
            protected void btnSubmit_Click(object sender, EventArgs e)
            {
            }
            protected void btnAdd_Click(object sender, EventArgs e)
            {
                Create(null);
            }
            public void Create(string id)
            {
                string targetId = id ?? Guid.NewGuid().ToString();
                myUserControl control = LoadControl("~/CustomControls/myUserControl.ascx") as myUserControl;
                control.ID = targetId;
                DynamicNameList.Controls.Add(control);
                SaveControlIdList();
            }
            public void Delete(Control control)
            {
                DynamicNameList.Controls.Remove(control);
                SaveControlIdList();
            }
            public void SaveControlIdList()
            {
                List<string> idList = new List<string>();
                foreach (Control control in DynamicNameList.Controls)
                {
                    idList.Add(control.ID);
                }
                ViewState["IdList"] = idList;
            }
            public string[] LoadControlIdList()
            {
                var list = (List<string>)ViewState["IdList"];
                if (list == null)
                {
                    return new string[0];
                }
                return list.ToArray();
            }
        }
        public interface IDynamicControlContainer
        {
            /// <summary>
            /// Deletes the specified control from the container
            /// </summary>
            /// <param name="control">The control.</param>
            void Delete(Control control);
        }
    }