ModalPopupExtender keep open

I have a ModalPopupExtender on a master page that makes a Panel visible when I click a button.  I have a checkbox in the Panel that is used in the query to display different rows in the GridView inside the Panel.  However, when I click the checkbox the panel disappears.  How do I keep the Panel visible and just Databind the GridView?  Code is below.

<asp:Button ID="LBtnChooseClient" runat="server" Text="Select or add a Client" Font-Size="Medium"></asp:Button><asp:ModalPopupExtender ID="ModalPopupExtender1" runat="server" PopupControlID="PanelPickPatient" 
                        TargetControlID="LBtnChooseClient" BackgroundCssClass="popUpStyle" 
                        DropShadow="True" RepositionMode="RepositionOnWindowResize"></asp:ModalPopupExtender> <asp:Panel ID="PanelPickPatient" runat="server" style="display:none;z-index:100000" BackColor="#FFFFFF" ScrollBars="Auto" Height="400"><table width="400" style="background-color: #FFFFFF"><tr><td><asp:Label ID="LblSelect" runat="server" Text="Select from list or " Font-Size="10pt" ForeColor="Blue"></asp:Label><asp:LinkButton ID="LBtnNewClient" runat="server" Text="Add a Client"></asp:LinkButton></td><td align="center"><asp:CheckBox ID="ckActiveOnly" runat="server" Text="Active" 
                        Checked="True" AutoPostBack="True" /></td><td align="right"><asp:LinkButton ID="LBtnCancelSelect" runat="server" Text="Cancel"></asp:LinkButton></td></tr></table><asp:GridView ID="gvPatients" runat="server" AutoGenerateColumns="False" 
            DataKeyNames="PatientID" DataSourceID="SqlselPatientsOneorg" 
            CellPadding="4" ForeColor="#333333" GridLines="None" ShowFooter="True"><RowStyle  CssClass="gridrow" /><Columns><asp:TemplateField HeaderText="Client Name"><ItemTemplate><asp:LinkButton ID="LBtnLastFirst" runat="server" ToolTip="click to select" 
                            Text='<%# Eval("LastFirst") %>' CausesValidation="False" CommandName="Select"></asp:LinkButton></ItemTemplate></asp:TemplateField><asp:BoundField DataField="DOB" DataFormatString="{0:d}" HeaderText="DOB" 
                    SortExpression="DOB" /><asp:TemplateField HeaderText="Unverified Meals" ItemStyle-HorizontalAlign="Center"><ItemTemplate><asp:LinkButton ID="LBtnUnverifiedMeals" runat="server" Text='<%# Eval("UnverifiedMeals") %>' 
                            CommandName="unmeals" CommandArgument='<%# Eval("PatientID") %>'></asp:LinkButton></ItemTemplate></asp:TemplateField><asp:TemplateField HeaderText="Unverified Snacks" ItemStyle-HorizontalAlign="Center"><ItemTemplate><asp:LinkButton ID="LBtnUnverifiedSnacks" runat="server" Text='<%# Eval("UnverifiedSnacks") %>' 
                            CommandName="unsnacks" CommandArgument='<%# Eval("PatientID") %>'></asp:LinkButton></ItemTemplate></asp:TemplateField><asp:TemplateField><ItemTemplate><asp:Label ID="LblPatientID" runat="server" Text='<%# Eval("PatientID") %>' CssClass="Hide"></asp:Label>    <asp:Label ID="LblAge" runat="server" Text='<%# Eval("Age") %>' CssClass="Hide"></asp:Label>    </ItemTemplate></asp:TemplateField></Columns><FooterStyle CssClass="gridfoot" /><PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" /><SelectedRowStyle BackColor="#FFFF99" Font-Bold="True" ForeColor="#333333" /><HeaderStyle CssClass="gridhead" /><EditRowStyle BackColor="#999999" /><AlternatingRowStyle CssClass="gridaltrow" /></asp:GridView><asp:SqlDataSource ID="SqlselPatientsOneorg" runat="server" 
            ConnectionString="<%$ ConnectionStrings:KetodataConnectionString %>" 
            SelectCommand="kd_selPatientsOneOrg" SelectCommandType="StoredProcedure"><SelectParameters><asp:CookieParameter Name="OrgID" CookieName="OrgID" Type="Int32" /><asp:ControlParameter Name="ActiveOnly" ControlID="ckActiveOnly" Type="Boolean" /></SelectParameters></asp:SqlDataSource></asp:Panel>