Dropbox is acknowledging a problem with syncing metadata heavy files like those in Scrivener. I've been syncing Scrivener files over Dropbox for sometime with no issue. Before, when I used SugarSync, I experienced this problem and it ultimately drove me to Dropbox. Regardless, I am taking new steps to keep local copies of all Scrivener files and encourage you to do so until Dropbox sorts this out.