Dropbox bug fix caused user files that were deleted after the 60 day deletion policy to reappear in the user's Dropbox folders. Usually, with the Dropbox Basic Users, files that have been deleted for more than 60 days will be removed from Dropbox and its servers. Ross S, a Dropbox employee, explained that a Dropbox bug prevented user files from being correctly removed from its servers and while fixing this bug some of the files were restored.

Reference | Dropbox Forum