How to make checkbox unchecked after page refresh?

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ASP.NET

In my form I have one checkbox (Unchecked state on load).by clicking this checkbox I have to load all the details in dropdown.if unchecked It will load minimum details in dropdown.
Problem:
At first, I have checked the checkbox then unchecked it.Then I just refreshing the page.
That time the checkbox become automatically checked. and other controls like radiobuttions in this page become disabled.Please help me to solve this problem.???
Code
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<asp:UpdatePanel ID="updChkAllPort" runat="server" UpdateMode="Always">
                                    <contenttemplate>
                        <div class="table_column_50" style="margin-left: -3px ! important"   runat="server"
                            id="divSelecAllPort">
                            <asp:CheckBox runat="server" ID="chListAllPort"  Checked ="false"  Text="List all ports" OnCheckedChanged="chListAllPort_changed" AutoPostBack="true" 
                                CssClass="checkbox-style" SkinID="label-style-data"  />
                        
                         </contenttemplate>

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// checkbox chaged
------------------------

protected void chListAllPort_changed(object sender, EventArgs e)
    {
        List<crewport> nextPort = new List<crewport>();
        nextPort = CrewReliefPlannerManager.CrewLastPortList(Convert.ToInt32(hidVesselId.Value), chListAllPort.Checked ? true : false);
        ddlPort.DataSource = nextPort;
        ddlPort.ValueField = "PortId";
        ddlPort.TextField = "PortName";
        ddlPort.DataBind();
        ddlPort.NullText = Resources.ErrorMessage.ResourceManager.GetString("Drop_Down_Select").ToString();

    }