iTextSharp - Cropping with PdfCleanUpProcessor works incorrectly

Question

I want to provide PDF redaction functionality by deleting contents within rectangular area. I use code from here: iTextSharp - Crop PDF File (C#)

static void textsharpie()
    {
        string file = "C:\\testpdf.pdf";
        string oldchar = "testpdf.pdf";
        string repChar = "test.pdf";
        PdfReader reader = new PdfReader(file);
        PdfStamper stamper = new PdfStamper(reader, new FileStream(file.Replace(oldchar, repChar), FileMode.Create, FileAccess.Write));
        List<PdfCleanUpLocation> cleanUpLocations = new List<PdfCleanUpLocation>();
        cleanUpLocations.Add(new PdfCleanUpLocation(1, new iTextSharp.text.Rectangle(0f, 0f, 600f, 115f), iTextSharp.text.BaseColor.WHITE));
        PdfCleanUpProcessor cleaner = new PdfCleanUpProcessor(cleanUpLocations, stamper);
        cleaner.CleanUp();
        stamper.Close();
        reader.Close();
    }

On some PDF documents this works incorrectly by changing the coordinates of some trimmed text lines (see attached images)

Before redaction:

After redaction:

Has anyone else encountered this problem?