Please create a numeric cell (with value set to e.g. 1232423 and style it with data format like this: # ##0 When you will open generated workbook (in MS Excel) you will see that the format has been modified to this: #\ ##0 The change cause that the number like -1232423 isn't formated as it should be, instead 1 232 423 we've got 1232 423 The problem doesn't exists when we open the workbook with Open Office Calc. I'm using MS Excel 2000 (Polish version).
Could you please create the same styling in Excel, and then check how POI sees this? Then, if you create that same format with POI in a new file, does it work properly in excel too?
No update for a long time, therefore resolving this bug for now, please reopen with the requested information based on an up-to-date version of poi.