Documents Repositories like Alfresco, SharePoint and so on are exposed as Liferay folders by Sync. If a users upload files to that folders entities get persisted to Liferay's DB rather than the repository. Accessing the repository via web interface or via Sync will lead to different results.
-Connect Liferay to a document repository (alfresco, sharepoint,...)
-Configure Sync to access the same Site.
Users accessing the portal via web interface can browse the repository
Users accessing the portal via sync gets an empty folder
-Upload a file via Sync (dummy.txt)
Users accessing the portal via web can not access the file uploaded via sync
Users accessing the portal via Sync can see only that file (dummy.txt)