In the event more than 3 rows contain formuls the following exception occurs:

There was 1 error:
1) testAddIntegers(org.apache.poi.hssf.usermodel.TestFormulas)
java.lang.ArrayIndexOutOfBoundsException
        at org.apache.poi.util.LittleEndian.putNumber(LittleEndian.java:536)
        at org.apache.poi.util.LittleEndian.putShort(LittleEndian.java:243)
        at
org.apache.poi.hssf.record.SelectionRecord.serialize(SelectionRecord.java:262)
        at org.apache.poi.hssf.model.Sheet.serialize(Sheet.java:584)
        at
org.apache.poi.hssf.usermodel.HSSFWorkbook.getBytes(HSSFWorkbook.java:522)
        at org.apache.poi.hssf.usermodel.HSSFWorkbook.write(HSSFWorkbook.java:474)
        at
org.apache.poi.hssf.usermodel.TestFormulas.testAddIntegers(TestFormulas.java:130)
        at org.apache.poi.hssf.usermodel.TestFormulas.main(TestFormulas.java:157)


oddly if I increase from 4 to 10 I get this instead:

There was 1 error:
1) testAddIntegers(org.apache.poi.hssf.usermodel.TestFormulas)
java.lang.ArrayIndexOutOfBoundsException
        at org.apache.poi.util.LittleEndian.putNumber(LittleEndian.java:536)
        at org.apache.poi.util.LittleEndian.putShort(LittleEndian.java:243)
        at
org.apache.poi.hssf.record.FormulaRecord.serialize(FormulaRecord.java:353)
        at
org.apache.poi.hssf.record.aggregates.ValueRecordsAggregate.serialize(ValueRecordsAggregate.java:174)
        at org.apache.poi.hssf.model.Sheet.serialize(Sheet.java:584)
        at
org.apache.poi.hssf.usermodel.HSSFWorkbook.getBytes(HSSFWorkbook.java:522)
        at org.apache.poi.hssf.usermodel.HSSFWorkbook.write(HSSFWorkbook.java:474)
        at
org.apache.poi.hssf.usermodel.TestFormulas.testAddIntegers(TestFormulas.java:130)
        at org.apache.poi.hssf.usermodel.TestFormulas.main(TestFormulas.java:157)

This is weird!