What you see is often caused by counterfeit flash drives that don't have the memory as advertized. These drives will act as if they are writing the data. But, in fact after using the 512 MB of real memory they are not. We see this mostly with large (64 GB) drive that have less than 1 GB of real memory. Kingston is one of the brands that is counterfeited. It is best to purchase Flash drives from a large retail store and avoid street markets with cheap prices;.