Det är ingen bug, det är en feature
Läs om kommandot mv på: http://www.unet.univie.ac.at/aix/cmds/aixcmds3/mv.htm
"You can use the mv command to move files within the same file system or between file systems. Whether you are working in one file system or across file systems, the mv command COPIES the file to the target and deletes the original file. The mv command preserves in the new file the time of the most recent data modification, the time of the most recent access, the user ID, the group ID, and the file mode of the original file."