It is most definitely not an iPod 5G.
That much is certain, there's absolutely no way that the installation could get this far if it were. So, we can put that one to bed, its definitely a Classic (read: 6/7G).
Now, for the problem:
If I were to speculate I would guess that you are using the system tray icon to eject the device.
Don't.
Its not really worth getting into /why/ this is an issue, and I'm not even terribly sure you'd care even if I did, so lets make this short. Don't use the system tray "safely eject" icon, instead eject the volume via right clicking from Explorer or My Computer.
[Saint]