Created attachment 23490 [details]
test.xlsm

I have two workbooks "test.xlsm" and "test.xls". I write following codes to set the cell "B2" to blank. The result behavior are different, XSSFWorkbook will clear the CellStyle of the blank cell but HSSFWorkbook won't.

--
Workbook source = (read "test.xlsm" or "test.xls")
Sheet sheet = source.getSheetAt(0);
Row row = sheet.getRow(1);
Cell cell = row.getCell(0);		
cell.setCellType(Cell.CELL_TYPE_BLANK);
source.write(...);
--

The expected behavior should follow HSSFWorkbook, i.e. CellStyle won't be clear since only cell value is set to blank.