I have two of these enclosures. When they are connected via USB 3.0 they do not spin down when the Mini is powered off. When connected via Firewire 800 they behave as expected: they spin down when the Mini is shut down. OWC provided a replacement enclosure and it does the same thing. OWC has not seen this problem with these enclosures that come with an installed drive. OWC also tried installing the same drive I use and it spins down. The drive in both enclosures is a 1TB Samsung. Has anyone else experienced this problem? I have read of similar problems with some other brands of external enclosures. Frankly, I can live with it: At the moment I have the enclosures connected via FW 800. If I elect to use USB 3.0 in the future I could simply turn them off manually. But I am hoping that the Macrumors "knowledge base" of users will have some suggestions about what is occurring and how I can fix this issue.