Override Price Recalculate Method in sales order

I need to maintain existing unit price when recalculate the price in sales order screen.

I created a table to maintain the price History.

table name - XXSOPriceHistory

SOOrderEntry extension query 

public PXAction<SOOrder> recalculateDiscountsAction;
    [PXUIField(DisplayName = "Recalculate Prices", MapEnableRights = PXCacheRights.Select, MapViewRights = PXCacheRights.Select)]
    [PXButton(CommitChanges = true, DisplayOnMainToolbar = false)]
    public virtual IEnumerable RecalculateDiscountsAction(PXAdapter adapter)
    {
      SOOrder order = Base.Document.Current;
      order.OrderDesc = "Testing1";

      XXSOPriceHistoryEntry sOPriceEntry = PXGraph.CreateInstance<XXSOPriceHistoryEntry>();



          XXSOPriceHistory toBeInserted = new XXSOPriceHistory();
          toBeInserted.LineNbr=1;
          toBeInserted.OrderNbr="SO1000";
          toBeInserted.InventoryID = 1435;

          toBeInserted = XXSOPriceHistoryData.Insert(toBeInserted);


      //sOPriceEntry.Save.Press();


      return Base.RecalculateDiscountsAction(adapter);
    }

When Click the recalculate button in sales order screen and click save , Same record add twice into the XXSOPriceHistory DAC.

Data Access query

#region TranID
    [PXDBIdentity(IsKey = true)]
    [PXUIField(DisplayName = "Tran ID")]
    public virtual int? TranID { get; set; }
    public abstract class tranID : PX.Data.BQL.BqlInt.Field<tranID> { }
    #endregion

    #region LineNbr
    [PXDBInt()]
    [PXUIField(DisplayName = "Line Nbr")]
    public virtual int? LineNbr { get; set; }
    public abstract class lineNbr : PX.Data.BQL.BqlInt.Field<lineNbr> { }
    #endregion

    #region OrderNbr
    [PXDBString(15, IsUnicode = true, InputMask = "")]
    [PXUIField(DisplayName = "Order Nbr")]
    public virtual string OrderNbr { get; set; }
    public abstract class orderNbr : PX.Data.BQL.BqlString.Field<orderNbr> { }
    #endregion

    #region OrderDate
    [PXDBDate()]
    [PXUIField(DisplayName = "Order Date")]
    public virtual DateTime? OrderDate { get; set; }
    public abstract class orderDate : PX.Data.BQL.BqlDateTime.Field<orderDate> { }
    #endregion

    #region InventoryID
    [PXDBInt()]
    [PXUIField(DisplayName = "Inventory ID")]
    public virtual int? InventoryID { get; set; }
    public abstract class inventoryID : PX.Data.BQL.BqlInt.Field<inventoryID> { }
    #endregion

Can I know why this happen and how to resolve it.