"LayoutProgress.LayingOut & Aborted" events are not handled on the UI thread, but other progress events are.

I am using the GViewer async rendering. I use below code to log info to a Label control.

It's strange that "LayoutProgress.LayingOut" is not handled on the UI thread.
But other prgress events are.

Maybe this is a bug?

The Progress event handler:

private void viewer_AsyncLayoutProgress(object sender, LayoutProgressEventArgs e)
{
    switch (e.Progress)
    {
        case LayoutProgress.Finished: // on the UI thread.
            Log(LogLevel.Info, "Graph rendered.");
            break;

        case LayoutProgress.Aborted: // NOT on the UI thread.
            Log(LogLevel.Error, "Graph rendering aborted.");
            break;

        case LayoutProgress.LayingOut: // NOT on the UI thread.
            Log(LogLevel.Info, "Graph laying out...");
            break;
        case LayoutProgress.Rendering: // on the UI thread.
            Log(LogLevel.Info, "Graph rendering...");
            break;
    }
}

The Log code:

public void Log(LogLevel logLevel, string msg)
{
    String header = "[INFO]: ";
    switch (logLevel)
    {
        case LogLevel.Error:
            header = "[ERROR]: ";
            break;
        case LogLevel.Info:
            header = "[INFO]: ";
            break;
        case LogLevel.Warning:
            header = "[Warning]: ";
            break;
    }

    String logMessage = header + msg + Environment.NewLine;
    if (!this.InvokeRequired) //<==== InvokeRequired == TRUE for "LayoutProgress.LayingOut & Aborted" events.
    {
        this.txt_output.AppendText(logMessage);
    }
    else
    {
        this.Invoke(new MethodInvoker(() => { this.txt_output.AppendText(logMessage); }));
    }
}

Start at the GViewer async rendering entry point and the AsyncLayoutProgress event handler, reproducing the reported thread behavior with the provided WinForms logging code. Trace how LayingOut, Aborted, Rendering, and Finished are dispatched; done means progress events have consistent UI-thread behavior or the documented behavior is clarified.