Created attachment 34834 [details]
file containing diffs between patched class and the original one

the problem is explained in the bug report 60803.

the solution i promote is to use a map into XSSFDataValidation to convert the Enums, which come from STDataValidation (range 1-3), into the ints exposed in DataValidation (range 0-2) so getErrorStyle returns values between 0-2.
This adjustment is required when we want to copy the errorstyle of a cell, or a group of cells, into another one : 

(working example with patch)
    newDataValidation.setErrorStyle(anotherDataValidation.getErrorStyle());


(working example without patch)
    newDataValidation.setErrorStyle(anotherDataValidation.getErrorStyle() - 1);