Problem with QwtPlotIntervalCurve

[SandyEmerald]

I' m using Qwt 6.0.1 undex Linux. Here's code example:

QwtPlotIntervalCurve *curve = new QwtPlotIntervalCurve("Test interval curve");
 
    QVector<QwtIntervalSample> samples;
    QwtIntervalSample *sample;
    sample = new QwtIntervalSample(DBL_MIN, 300, 700);
    samples.push_back(*sample);
    sample = new QwtIntervalSample(DBL_MAX, 300, 700);
    samples.push_back(*sample);
 
    curve->setSamples(samples);
    curve->setStyle(QwtPlotIntervalCurve::Tube);
 
    curve->attach(ui->plot);
 
    ui->plot->replot();

QwtPlotIntervalCurve *curve = new QwtPlotIntervalCurve("Test interval curve");

    QVector<QwtIntervalSample> samples;
    QwtIntervalSample *sample;
    sample = new QwtIntervalSample(DBL_MIN, 300, 700);
    samples.push_back(*sample);
    sample = new QwtIntervalSample(DBL_MAX, 300, 700);
    samples.push_back(*sample);

    curve->setSamples(samples);
    curve->setStyle(QwtPlotIntervalCurve::Tube);

    curve->attach(ui->plot);

    ui->plot->replot();

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After running i saw this:
plot1.png

and after i made right-click (i have default QwtPlotZoomer) i saw this:
plot2.png

So, how i can set infinite interval curve, Uwe?