When evaluation an SXSSFCell containing a formula, the value of the cell is always cleared. 
In the following code, I would expect the output to be 3.0, but it is 0.0. If I instead created the Workbook as an XSSFWorkbook, the code works as expected.

final Workbook wb = new SXSSFWorkbook();
final Cell cell = wb.createSheet().createRow(0).createCell(0);
cell.setCellFormula("1+2");
wb.getCreationHelper().createFormulaEvaluator().evaluateInCell(cell);
System.out.println(cell.toString());
wb.close();