The coordinate of QPdfSelection seems like to be wrong when pdf page contains non-displayable area

QPdfSelection QPdfDocument::getAllText(int page)
{
    const QPdfMutexLocker lock;
    FPDF_PAGE pdfPage = FPDF_LoadPage(d->doc, page);
    double pageHeight = FPDF_GetPageHeight(pdfPage);
    FPDF_TEXTPAGE textPage = FPDFText_LoadPage(pdfPage);
    int count = FPDFText_CountChars(textPage);
    if (count < 1)
        return QPdfSelection();
    QString text = d->getText(textPage, 0, count);
    QList<QPolygonF> bounds;
    QRectF hull;
    int rectCount = FPDFText_CountRects(textPage, 0, count);
    for (int i = 0; i < rectCount; ++i) {
        double l, r, b, t;
        FPDFText_GetRect(textPage, i, &l, &t, &r, &b);
        QRectF rect(l, pageHeight - t, r - l, t - b);
        if (hull.isNull())
            hull = rect;
        else
            hull = hull.united(rect);
        bounds << QPolygonF(rect);
    }
    qCDebug(qLcDoc) << "on page" << page << "got" << count << "chars," << rectCount << "rects within" << hull;    FPDFText_ClosePage(textPage);
    FPDF_ClosePage(pdfPage);    return QPdfSelection(text, bounds, hull, 0, count);
}