Created Unassigned: Update an exists Excel File,Some cell's backgroud color of the Excel became black . [13497]

Code like below:
FileStream file = new FileStream(@"D:\npoi\BeforeSave.xlsx", FileMode.Open, FileAccess.Read);
XSSFWorkbook hssfworkbook = new XSSFWorkbook(file);
FileStream file1 = new FileStream(@"D:\npoi\AfterSave.xlsx", FileMode.Create);
hssfworkbook.Write(file1);
file1.Close();

the Referance File is in the attachments file (bug.rar)