When I sync Google Drive, all my files are downloaded and converted to local files without problems. I use comments a lot and they are included in docx/odt files - when I add content and comments via Google Docs web interface, they appear on my local copies.
But if I edit a local file and then save, it gets sync and ALL comments in that file are deleted in the Google Web version!
This happens every time and works both with docx and odt files, both in Libre Office 4.3 and 5.1.