Abot 1.2.3 with multiple threads is not stopping with CancellationTokenSource

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I am using the latest Abot 1.2.3 via NuGet.
Maybe I am doing something wrong but the following code does not stop the crawl process:

    CancellationTokenSource cts = new CancellationTokenSource();

    private void btnStart_Click(object sender, EventArgs e)
    {
        BackgroundWorker bgw = new BackgroundWorker();
        bgw.DoWork += bgw_DoWork;
        bgw.RunWorkerCompleted += bgw_RunWorkerCompleted;
        bgw.RunWorkerAsync();
    }

    void bgw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        //never reaches this point
    }

    void bgw_DoWork(object sender, DoWorkEventArgs e)
    {
        PoliteWebCrawler crawler = new PoliteWebCrawler();
        crawler.PageCrawlCompletedAsync += crawler_PageCrawlCompletedAsync;
        CrawlResult result = crawler.Crawl(new Uri("http://www.finanzen-forum.net"), cts);
    }

    void crawler_PageCrawlCompletedAsync(object sender, PageCrawlCompletedArgs e)
    {

    }

    private void btnStop_Click(object sender, EventArgs e)
    {
        cts.Cancel();
    }

The problem only occurs when you have set multiple threads (in my case 20 threads) and you have to let the crawler run a bit (15 seconds was enough to reproduce the problem).

If you are using 1 thread, it works.

I know that you have to wait a bit, depending on how much threads you have started but I have waited for over a minute for Abot to end all 20 threads. No success.