Disappearing Reappearing Files

Hi Everyone.

Something weird is happening with my new 2tb My Book Studio (for Mac). I copy files across to the drive, it hums away and the copy finishes. But when I go into the folder, the files aren’t there. Get Info says the folder contains all the files (and is the right size on the disk) but I can’t see anything. When I try to re-copy the files across I get asked “this file already exists, do you want to replace it?” … Then I click “no” and suddenly all the files are there again.

Even if the files do eventually reappear, it doesn’t fill me with confidence. Anyone know what’s going on?

The drive is Mac formatted using FW800. The computer is a 24" Intel iMac on OSX Tiger 10.4.11