dragon as isp not working in arduino IDE v. 1.05

environment: ubuntu 14.04, arduino 1.05 dfsg2

symptoms:
when burning bootloader with avr dragon in isp mode the IDE fails:

         Using Port                    : usb
         Using Programmer              : dragon_isp
avrdude: stk500v2_dragon_isp_open()
avrdude: usbdev_open(): did not find any USB device "usb"

a little up in the log there is (in white) the command parsed to avrdude:

/usr/share/arduino/hardware/tools/avrdude -C/usr/share/arduino/hardware/tools/avrdude.conf -v -v -v -v -patmega32u4 -cdragon_isp -Pusb -Uflash:w:/usr/share/arduino/hardware/arduino/bootloaders/caterina/Caterina-Leonardo.hex:i -Ulock:w:0x2F:m

If I paste the white part in a terminal, everything works and the bootloader is burned on the chip.

my programmers.txt file contains:

dragon.name=Atmel AVR Dragon in ISP mode
dragon.communication=usb
dragon.protocol=dragon_isp

what goes wrong?