certain timeframe bars are not loading up to the current index

This program overlays an alternative timeframe bars source onto the chart, the problem is only a certain number of selected timeframes are working correctly i.e, are being drawn up to the last index in the series like this : (chart timeframe = 1h , alternate timeframe  =  6h)

But say for (chart timeframe = 1h, alternate timeframe = 4h)  it shows up like this:

only when I manually zoom out the chart and more bar history is loaded, the drawings are correct like this :

why is this occurring ? 

here's my code:

using System;
using cAlgo.API;
using cAlgo.API.Internals;
using cAlgo.API.Indicators;
using cAlgo.Indicators;

namespace cAlgo
{
    [Indicator(IsOverlay = true, TimeZone = TimeZones.UTC, AccessRights = AccessRights.None)]
    public class TimeFrame_Candles : Indicator
    {
        [Parameter("Time Frame", DefaultValue = "TimeFrame.Hour")]
        public TimeFrame time_frame { get; set; }

        Bars bars_source;
        int last_index;

        DateTime open_time;
        DateTime close_time;

        double open;
        double close;
        double high;
        double low;
        string color;
        int type;

        protected override void Initialize()
        {
            bars_source = MarketData.GetBars(time_frame, SymbolName);
            last_index = 0;
        }

        public override void Calculate(int index)
        {
            if (index > last_index)
            {
                var x = bars_source.OpenTimes.GetIndexByTime(bars_source[last_index].OpenTime);
                bool index_in_range = indexinrange(x);

                if (index_in_range && x != -1)
                    on_candle_close(x);
                else
                    return;
                last_index = index;
            }
        }

        private void on_candle_close(int x)
        {
            open_time = bars_source[x].OpenTime;
            close_time = bars_source[x + 1].OpenTime;

            open = bars_source[x].Open;
            close = bars_source[x].Close;
            high = bars_source[x].High;
            low = bars_source[x].Low;

            type = close > open ? 1 : close < open ? 0 : 2;

            color = type == 1 ? "Green" : type == 0 ? "Red" : "DimGray";

            var rect = Chart.DrawRectangle("draw_no" + x.ToString(), open_time, open, close_time, close, color, 3);
            rect.IsFilled = false;
            Chart.DrawText("text" + x.ToString(), x.ToString(), bars_source[x].OpenTime, bars_source[x].Close, "Black");

        }


        private bool indexinrange(int index)
        {
            var last_index = bars_source.Count - 1;
            if (index < last_index)
                return true;
            else if (index >= last_index)
                return false;
            return false;

        }
    }
}

thank you