Surely defective card. Very low transfer rates and data loss when the card is ejected (properly). Tested by copying from a PC to a Win 8.1 GS4 connected via USB, and then copy to the card mounted on the PC and copy directly from the internal memory of the card GS4 ers. Same result, the data disappear. Map exchanged by a new one (in a new package, so surely another series). The card is not recognized by any device (GS4 2, 2 and 1 PC Linux).