Created attachment 101602 [details]
sample file

Problem description: 
When using the group/ungroup feature for columns, if the file is saved as .xlsx with column range grouped(collapsed) then after reopening the file, columns will be gone.
No folding button and ctrl+F2 won't work. Content can be still accessed through format->Column->show.
Looks like Collapsed="true" needs to be set.

If the file is open with Microsoft Office, it will suggest to repair the file due to improper  column naming and result in data lose.


Steps to reproduce:
1. Create a file with a few columns and group them.
2. Save the file as xlsx.
3. Open the file.

Current behavior:
Columns are hidden but not folded.

Expected behavior:
Folded columns/rows with the appropriate buttons/menus.

              
Operating System: Debian
Version: 4.2.4.2 release