Dropdown style broken inside UpdatePanel

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C#

ASP.NET

Ajax

UpdatePanel

Hi,
I have 2 dropdownlist within the updatepanel when I select a item from dropdownlist another list change according to another ddl.

This is my aspx code

<asp:UpdatePanel runat="server" ID="pnlModalFirst" UpdateMode="Conditional">
                            <ContentTemplate>
                                <div class="modal-body">
                                    <asp:DropDownList runat="server" CssClass="selectpicker markaselect margin-bottom-10" ID="ddlBrand" ClientIDMode="Static" DataValueField="Id" DataTextField="BrandName" AutoPostBack="True" OnSelectedIndexChanged="ddlBrand_SelectedIndexChanged" title="Marka Seçiniz" data-live-search="true" />
                                    <asp:DropDownList runat="server" CssClass="selectpicker modelselect margin-bottom-10" ID="ddlModel" ClientIDMode="Static" AutoPostBack="True" OnSelectedIndexChanged="ddlModel_SelectedIndexChanged" title='Model Seçiniz' />
                                    <asp:DropDownList runat="server" CssClass="hidden selectpicker margin-bottom-10" ID="ddlKaroser" title='Karoser Seçiniz' />
                                    <asp:Button runat="server" CssClass="col-md-2 btn-block btn-u btn-u-blue btn-u-lg " ID="btnDKnow" Text="Teklifleri Al" OnClick="btnDKnow_Click" ValidationGroup="modalKnow" />
                                </div>
                            </ContentTemplate>
                            <Triggers>
                                <asp:AsyncPostBackTrigger ControlID="ddlBrand" EventName="SelectedIndexChanged" />
                                <asp:AsyncPostBackTrigger ControlID="ddlModel" EventName="SelectedIndexChanged" />
                            </Triggers>
                        </asp:UpdatePanel>

And also I use [this] plugin my dropdownlist but when I change first ddl all style broken like this

Before select ddl
http://imgur.com/GwKY8wg[^]

After select ddl

http://imgur.com/Zqhev2e[^]

Do you have any suggestion.