Update Panel in Repater Textbox Blank.

Hi, I entered Textbox but When I click LinkButton is Textbox blank coming. Why ? How can I do.

İmportant = This example Update Panel and in Repater.

Html Code below.

<div class="panel panel-default"><asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager><asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Always"><ContentTemplate><asp:Repeater ID="rptyorumlar" runat="server" ClientIDMode="AutoID"><ItemTemplate><div class="panel-body"><div class="col-md-12 nosag nosol"><div class="col-md-6 text-left nosag nosol"><div class="comment-user"><i class="fa fa-user"></i>&nbsp;<b><%#Eval("UserID") %></b></div><time><i class="fa fa-clock-o"></i>&nbsp;<span style="color: #ddd;"><%#Eval("Tarih") %></span></time></div><div class="col-md-6 text-right nosag nosol"><div class="comment-user"><i class="fa fa-comment-o"></i>&nbsp;<b><%#Eval("ID") %></b></div></div></div><div class="comment-post"><p><%#Eval("Yorum") %></p></div><div class="col-md-6 nosag nosol"><div class="col-md-3 nosag nosol"><asp:Label ID="lblId" runat="server" Text='<%#Eval("ID") %>' Visible="false" /><span style="font-size: 19px;"><asp:LinkButton ID="lnkbegen" data-toggle="tooltip" data-placement="bottom" title="Beğendim" runat="server" OnClick="lnkbegen_Click"><i class="fa fa-futbol-o"></i> </asp:LinkButton><span class="count-icon"><span class="count" style="right: 5px;"><%#Eval("Begen") %></span></span></span></div><div class="col-md-3 nosag nosol"><asp:Label ID="lblad" runat="server" Text='<%#Eval("ID") %>' Visible="false" /><span style="font-size: 19px;"><asp:LinkButton ID="lnkbegenme" class='<%#Eval("ID") %>' data-toggle="tooltip" data-placement="bottom" title="Beğenmedim" runat="server" OnClick="lnkbegenme_Click"><i class="fa fa-heartbeat"></i></asp:LinkButton><span class="count-icon"><span class="count" style="right: 5px;"><%#Eval("Begenme") %></span></span></span></div></div><div class="col-md-6 nosag nosol text-right"><span style="font-size: 19px;"><a href="#" class="dropdown-toggle" data-toggle="dropdown"><i class="fa fa-bug"></i></a><ul class="dropdown-menu" style="border: 1px solid; border-color: #D5D5C9; padding: 5px; margin-top: -85px;"><div><div class="form-group"><asp:TextBox ID="txtsikayet" Rows="2" CssClass="form-control" runat="server"></asp:TextBox></div><div class="form-group" style="padding-top: 0px;"><asp:LinkButton ID="lnksikayetet" CssClass="btn btn-info btn-block" runat="server" OnClick="lnksikayetet_Click">Şikayet</asp:LinkButton></div></div></ul></span></div></div><hr /></ItemTemplate></asp:Repeater></ContentTemplate></asp:UpdatePanel></div>

Link button code behind.

 protected void lnksikayetet_Click(object sender, EventArgs e)
        {


            LinkButton lnkk = sender as LinkButton;

            int id = int.Parse(((lnkk.NamingContainer).FindControl("lblid") as Label).Text);
            string sikayet = (lnkk.NamingContainer.FindControl("txtsikayet") as TextBox).Text;                


            using (Entities tri = new Entities())
            {
                Sikayet sk = new Sikayet
                {

                    Sikayet1 = sikayet,
                    Tarih = DateTime.Now,
                    YorumID = id,
                    UserID = 3

                };

                tri.Sikayet.Add(sk);
                tri.SaveChanges();
                Response.Write("<script LANGUAGE='JavaScript' >alert('Kayıt Eklenmiştir...')</script>");

            }
        }