Chart.RemoveObject not always working in Backtesting

When Chart.RemoveObject is called in Backtesting mode the chart objects are not always removed. This used to work fine in an earlier version and can also be replicated in RealTime mode if it is left to run for long enough. Tested on Spotware version 4.3.11

The below example code draws a line from between previous candles OnBar and removes the previously drawn line.

The behaviour seems to be racing as different lines are not deleted each run.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using cAlgo.API;
using cAlgo.API.Collections;
using cAlgo.API.Indicators;
using cAlgo.API.Internals;

namespace cAlgo.Robots
{
    [Robot(AccessRights = AccessRights.None)]
    public class DrawDeleteLines : Robot
    {
        [Parameter("Timeframe0", DefaultValue = "Minute")]
        public TimeFrame tf0 { get; set; }


        TimeFrame[] Frames = new TimeFrame[1];
        Bars[] series = new Bars[1];
        
        protected override void OnStart()
        {
            Chart.RemoveAllObjects();
            Frames[0] = tf0;
            series[0] = MarketData.GetBars(Frames[0]);
            
        }

        protected override void OnBar()
        {
            // Handle price updates here
            var line1 = Chart.DrawTrendLine(Frames[0] + "-" + (series[0].Count - 4) + "-" + (series[0].Count - 2), series[0].OpenTimes[(series[0].Count - 4)], series[0].LowPrices[(series[0].Count - 4)], series[0].OpenTimes[(series[0].Count - 2)], series[0].HighPrices[(series[0].Count - 2)], Color.Red);
            line1.IsInteractive = true;
            Chart.RemoveObject(Frames[0] + "-" + (series[0].Count - 5) + "-" + (series[0].Count - 3));
        }



        protected override void OnStop()
        {
            // Handle cBot stop here
        }
    }
}