It's a bug. Drives attached via Firewire, USB or a PCI controller will show as removable. Worse, if you logout, they will dismount. You can SSH in and try to access the drives and they will be gone.
I opened a Radar bug report on it, but it has not been fixed yet. (I haven't tried it in 10.3.2, but I assume that's what you're talking about)
Wade