PDF Radio Buttons Resizing on Flatten()

We have a PDF form which contains a number of radio buttons. The radio buttons are all the same size, but when we Flatten() the PDF the last radio button increases in size slightly. I have attempted to open and just resave the PDF as a new document and the radio button does not change size. It's only when I flatten the document that it changes size.

static void Main(string[] args)
        {
            License l = new License();
            l.SetLicense("Aspose.Total.lic");
            byte[] document = File.ReadAllBytes("PTS_Form_2014_v1.3a.pdf");
            Document pdfDocument = new Document(new MemoryStream(document));
            pdfDocument.Flatten();
            FileStream fs = new FileStream("PTS_Form_Flattened.pdf", FileMode.Create);
            pdfDocument.Save(fs);
        }