If I use HSSFSheet#shiftRows() it will not copy the CellStyle of the row befor. 

I fix it very bad and slowly this way:
public void insertRowAfter(int rowNum) {
		HSSFRow row = sheet.getRow(rowNum);
		sheet.shiftRows(rowNum + 1, sheet.getLastRowNum(), 1, true, true);
		
		HSSFRow newRow = sheet.getRow(rowNum + 1);
		for (short i = 0; i <= row.getLastCellNum(); i++) {
			HSSFCell cell = row.getCell(i);
			HSSFCell newCell = newRow.getCell(i);
			if (cell != null) {
				if (newCell == null)
					newCell = newRow.createCell(i);
				newCell.setCellStyle(cell.getCellStyle());
			}
		}
	}

Is this a bug- or future- request?