Well, maybe because Windows computer in your library has virus(es)?
In my country (Indonesia), there are so many viruses that make null folder in flash disk, and move any files in flash disk to it.
Seeking solution to Windows messing with flash drive
Size does matter. Older digital cameras (and probably other older devices that use flash memory, if there are any) can't use newer large capacity flash memory cards. Sometimes a firmware upgrade will fix that.B.K. Johnson wrote:...Last week the library computer (Windows version unknown) couldn't open a SanDisk Cruzer 8Gb drive. This drive had the unnamed directory/folder. Their computer was able to access files on a SanDisk Cruzer 4Gb which doesn't have the null directory in the root. Both of these drives were originally factory formatted, so Gparted is not involved. Could the size have mattered? ...
Also, older SD card readers (SD-to-USB converters) won't work with newer SD cards above a certain size. I don't know if this is planned obsolescence or a boneheaded lack of forethought on the part of the designers.