This is an issue with Mac OS X and all PCIe USB cards connected to a storage device in a Mac Pro or PowerMac G5. This applies to the USB ports in the Sonnet Tango FireWire/USB PCIe, Tango FireWire 800/USB PCIe and Allegro Express USB 2.0 cards. Sonnet has notified Apple, who has declined to address this issue at this time.