Bug 27405

isnumber(), isblank(), istext(), all evaluate correctly when used in cell 
formulas on their own. However if they are placed in if statements, ( if( 
isnumber(a1),a1,a2) for example) the result is always false (i.e. the second 
term).

This is still the case in version 2.5

The following code fragment illustrates the problem, creating sheet with 4 
cells, B1 & B2 initially set to 1 and 999, and B5 & B6 containing isnumber
(b1), and if(isnumber(b1), b1, b2) respectively.

B5 always reflects the state of b1, but b6 always shows the value in b2. 
Editing the formula in excel "fixes" the problem.

    HSSFWorkbook wb = new HSSFWorkbook( );
    HSSFSheet sheet = wb.createSheet("input");
    // input row 0
    HSSFRow row = sheet.createRow((short)0);
    HSSFCell cell=row.createCell((short)0);
    cell = row.createCell((short) 1);
    cell.setCellValue(1);
    // input row 1
    row = sheet.createRow((short)1);
    cell = row.createCell((short)1);
    cell.setCellValue(999);

    int rno = 4;
    row = sheet.createRow(rno);
    cell = row.createCell((short)1);
    cell.setCellFormula("isnumber(b1)");
    cell = row.createCell((short)3);
    cell.setCellFormula("IF(ISNUMBER(b1),b1,b2)");

    try{
      FileOutputStream fileOut = new FileOutputStream("c:\\workbook.xls");
      wb.write(fileOut);
      }
    catch (IOException e) {System.err.println("Error in write 
xl: "+e.getMessage()); }