This is a problem that happened with two USB sticks that I used in the Sky decoder to record programming. When the stick is used again in Windows you need to format it with the FAT32 file system (or other supported by Windows), as the Sky uses a file system unknown to. I do not know if it's owner, if some version of ext, etc. and does not really matter, because the programming is encrypted and recorded far as I know there is no way to use it in any other way than playing the same decoder that made the recording. The fact is that to the stick again have utility in computers you need to format it.
The problem is that Windows will indicate that the flash drive has only 512MB and you can only format it with this ability. In my case, both times the problem occurred were flash drives from Sandisk 32GB. I do not know if the problem also occurs with other brands and sizes, but probably yes.
The solution was given by technical support itself and Sandisk is to use the program HP Disk Storage Format Tool para formatar o pendrive com seu tamanho verdadeiro. Once formatted with this application, the flash drive can be used normally again.