Deleting files when copying using USB port

[Norwegian2]

I live in Norway where we use letters Æ (A+E), Ø (O+E), A (A+A).
When I was copying files from a portable hard drive. After copying were done all files and folders with these letters were removed from the portable hard drive. They had not been copied to the NAS.
Do anyone have a suggestion what to do?

NAS mod: QNAP TS-469L