Why GlyphRectangle bounding box not correct for letter g?

[hjy1210]

I have a sample pdf file helloworld.pdf, which have one single line "Hello, good morning!".

Use the following code to draw bounding box of each letter.

            using (var document = PdfDocument.Open("helloworld.pdf"))
            {
                var builder = new PdfDocumentBuilder { };
                for (var pageNumber = 1; pageNumber <= document.NumberOfPages; pageNumber++)
                {
                    var pageBuilder = builder.AddPage(document, pageNumber);
                    pageBuilder.SetStrokeColor(128, 128, 128);
                    var page = document.GetPage(pageNumber);
                    
                    var letters = page.Letters; 
                    foreach (var letter in letters)
                    {
                        if (letter != null)
                        {
                            pageBuilder.DrawLine(letter.GlyphRectangle.BottomLeft, letter.GlyphRectangle.BottomRight, 0.3);
                            pageBuilder.DrawLine(letter.GlyphRectangle.BottomRight, letter.GlyphRectangle.TopRight, 0.3);
                            pageBuilder.DrawLine(letter.GlyphRectangle.TopRight, letter.GlyphRectangle.TopLeft, 0.3);
                            pageBuilder.DrawLine(letter.GlyphRectangle.TopLeft, letter.GlyphRectangle.BottomLeft, 0.3);
                        }
                    }
                }
                byte[] fileBytes = builder.Build();
                File.WriteAllBytes("helloworld-letterbox.pdf", fileBytes); 
            }

Result is:

Note: the bounding box do not include the descent part of letter g.

[EliotJones]

This definitely looks like a bug, not sure when I'd have time to look so unfortunately it'll probably be stuck like this for a good-while.