When you buy cheap USB Bluetooth dongles, that they have the same device address (MAC). The tool bdaddr can be used to change these addresses.

bdaddr - Utility for changing the Bluetooth device address

Usage:
	bdaddr [-i <dev>] [-r] [-t] [new bdaddr]

To change the dongles address, connect only the one you want to modify and run:

$ bdaddr F4:4E:FD:B8:A4:14

Unplug and replug the dongle, bluetoothd should now be able to configure both USB Bluetooth dongles.