Problem description: If you add a new comment to a cell, the existing comments of other cells disappear after closing and open the file again.

Steps to reproduce:
1. Create a new spreadsheet file
2. write "123" in one of the cells
3. add comment "123" to that cell
4. save and close the file
5. open the file
6. write "123" to another blank cell
7. add comment "123" to that cell
8. save and close the file
9. open the file again

Current behavior:
The first comment has disappeared!

Expected behavior:
all comments should be saved!
              
Operating System: Windows 7
Version: 4.2.0.4 release
Last worked in: 4.1.4.2 release