Consider the following scenario:
You use Microsoft Office Communications Server 2007 R2, Group Chat client to post a text file in a channel.
You post another text file which has the same file name as the file that you just posted. The second text file has less content than the first text file.
You use the Open option to download and open the first text file.
After you open the first text file, you use the Open option to open the second text file.
In this scenario, the opened file contains the full content of the second text file, and part of the content of the first text file.
This issue occurs because a file in a temporary folder has the same file name as the file that is downloaded. When the Group Chat client users click Open to download the file, the Group Chat client replaces bytes in the existing file, and then creates a merged file.
To fix this issue, install the following cumulative update:
2549043 Description of the update for the Office Communications Server 2007 R2 Group Chat client: June, 2011