OS X stores special characters in Normalization Form Canonical Decomposition (NFD), i.e. for example german umlauts are stored as two characters ("ä"" -> a, U+0308). When syncing with a Linux client, this decomposition is also synced, so umlauts are stored in NFD on Linux also, while the rest of the Linux system stores in NFC ("ä" as one single character U+00E4). Even worse, in some situations this leads to the same file being stored twice on the Linux filesystem, once in NFD and once in NFC(as these are two different filenames). I don't know if there is an elegant solution for this, and I don't know how other sync clients (Dropbox, ownCloud) handle this.