checkmarks are displaying while move to previous page in asp.net gridview

protected void gvFiling_PageIndexChanging(Object sender, GridViewPageEventArgs e)
        {
            List<DataKey> datakeys = new List<DataKey>();
            foreach (GridViewRow row in gvFiling.Rows)
            {
                if (((CheckBox)row.FindControl("cbxApply")).Checked)
                {
                    datakeys.Add(gvFiling.DataKeys[row.RowIndex]);
                }
                else
                    datakeys.Remove(gvFiling.DataKeys[row.RowIndex]);
            }
            if (SessionWrapper.RelatedFilingsRecordsList != null)
            {
                List<DataKey> sessionList = new List<DataKey>();
                sessionList = SessionWrapper.RelatedFilingsRecordsList;

                foreach (DataKey dk in datakeys)
                {
                    foreach (GridViewRow row in gvFiling.Rows)
                    {
                        sessionList.Add(dk);
                    }
                }
                SessionWrapper.RelatedFilingsRecordsList = sessionList;
            }
            else
                SessionWrapper.RelatedFilingsRecordsList = datakeys;
        }

public static List<System.Web.UI.WebControls.DataKey> RelatedFilingsRecordsList
    {
        get
        {
            if (HttpContext.Current.Session["RelatedFilingsRecordsList"] != null)
                return (List<System.Web.UI.WebControls.DataKey>)HttpContext.Current.Session["RelatedFilingsRecordsList"];
            else
                return null;
        }
        set
        {
            HttpContext.Current.Session["RelatedFilingsRecordsList"] = value;
        }
    }