A Sun Fire B10n blade can be part of a high-availability load-balancing pair. In other words, the device is the child of a logical device that has a type that is subtype of device type halb. If you run the shelfsync command on the shelf that contains this blade, the shelfsync command reports the device as a newly discovered device. If you then choose to add this new device, the command reports a message while adding the device to the database. The message tells you that a device with the same MAC address is present in the database.
Workaround: Ignore the message.