Excel XLSX export creates corrupt files in 4.0.1

[talonkrass]

I've updated to JasperReports 4.0.1 in my current Java implementation (from 3.7.4), and I've got a new problem.  XLSX files are being reported as corrupt by Excel, and when you open them, the dates are unformatted numbers.

The only way I've found to fix it so far is to set IS_DETECT_CELL_TYPE to false in the exporter.

I would really like to use IS_DETECT_CELL_TYPE to get real numbers and dates in my spreadsheets, rather than strings.  Is there a way to get it to work?

[talonkrass]

 I was using the JRXlsxExporter when this problem occurred.  I've found switching to the JExcelApiExporter to export XLS files works with IS_DETECT_CELL_TYPE set to true.