Initial steps:

• Use the Office Connector with Excel documents stored as attachments
• Set the excel file to Review -> Share Workbook.

After doing above steps, following is the scenario of the issue:
If two users have the excel workbook open and user_a makes a change and saves, and user_b makes change and saves.
It results two different versions w/o the merged results.
(As opposed to user_b's save including user 1's change)

Thanks in advance.