We are publishing some daily excel report to our users via Force.com content by uploading new version of each docs. 

From Summer '12, we encountered an issue on force.com content.

When we uploaded new version of daily reports, sometime some of them have been disappeared and after that none can search and find them on Force.com content.

Actually, those disappeared docs had not been deleted. If users know the exact URL link for each docs, we can access to them by clicking exact URL link for each docs. But it is not available to search them by keyword and also they are not listed in the library view. So there is not way to access those disappeared document other than knowing direct access URL link for each document.

I already reported salesforce support team on June 12th, 2012, but at this time they have not provided any solution and find out bottom cause of this issue. 

Our company tried to start registering many business documents on force.com contents, but by this issue, some users show increasing skepticism for the security and function of force.com content.

Is there anyone who encountered similar cases? Or Is there someone who know the information about bottom cause?

Thank you in advance.