I am using POI (Java API for Microsoft Documents) and Microsoft Excel 2008/2010 to create Excel Documents with Custom Properties. The properties can be viewed perfectly in Libre Office via File->Properties then the Custom Properties Tab.
Problem is if you make any changes to the file and hit save all the Custom Properties are cleared. This does not happen when Editing a file in Microsoft Excel 2008/2010. I have been able to reproduce this on LibreOffice 3.5.7.2 and LibreOffice 4.0.2.2
How to reproduce:
Use Microsoft Office Excel 2010/2008 create new Excel Spreadsheet. Add data to any cell. Add custom properties to the Spreadsheet E.g Key=SuperKey, Value=123456, ValueType=Text.
Open the file in LibreOffice 3.5.7.2 or 4.0.2.2 view the Custom Properties on the file. This will work perfect.
Edit any cell in the spreadsheet and hit save and exit.
If you op the file in Microsoft Office or Libre Office the custom properties are gone.
Edit:
Forgot to added using xlsx file format.
No need is a known bug : https://bugs.freedesktop.org/show_bug.cgi?id=54831