File corruption with OO 1.9.109

Dear OO developers

I created a spreadsheet with the 109 beta of OpenOffice 2.0 and saved 
it as t1.ods. I then right-clicked on this file and renamed it to 
t1.zip. I then right-clicked on it again and used the Windows zip 
extraction tool to unpack it. I did not open or in any way alter the 
resulting directory or contents thereof. I right clicked on the 
folder, compressed as a zip and then renamed the result to t1.ods.

When I try to open this file with OpenOffice, it reports it is 
corrupt and offers to repair the file. When I answer "yes" it then 
reports it cannot repair the file.

When I unzip both the before and after versions of the ods file, the 
results are identical. When I examine the two ods files using a hex 
editor, I see that both are zip files (PK first 2 chars), but the 
file produced by OpenOffice has some plain text XML inside it 
(manifest)!

What am I doing wrong? I would like to be able to programmatically 
generate ods files and performed these above manual steps first as a 
test. If I can generate ods files from my application which are 
subsequently editable in OpenOffice, this would be of great help to 
my users and will be a compelling reason for them to switch from 
their present proprietary office suite to open office.

Thanks for any help. I am using Windows XP SP2.

Regards

David