Flashing efuse verification error...

[DeDuckProject]

Hi again,
I'm trying to flash HIDuino to my Arduino Uno (with ATmega328P and ATmega16u2).
I'm using an arduino pro mini as an ISP (if that changes anything..)

Following these commands:

avrdude -p ATmega16U2 -F -P /dev/tty.usbserial-A9SZZT51 -c avrisp -b 19200 -U flash:w:HIDUINO_MIDI.hex -U lfuse:w:0xFF:m -U hfuse:w:0xD9:m -U efuse:w:0xF4:m -U lock:w:0x0F:m

The following error appears:
avrdude: 1 bytes of efuse written
avrdude: verifying efuse memory against 0xF4:
avrdude: load data efuse data from input file 0xF4:
avrdude: input file 0xF4 contains 1 bytes
avrdude: reading on-chip efuse data:

Reading | ################################################## | 100% 0.02s

avrdude: verifying ...
avrdude: verification error, first mismatch at byte 0x0000
0xfc != 0xf4
avrdude: verification error; content mismatch

avrdude: safemode: efuse changed! Was f4, and is now fc

---

the other fuses are verified ok, and when I remove -U efuse:w:0xF4:m from the command line there are no errors whatsoever but HIDuino probably isn't flashed right and doesn't work.
note that I get this error after running the command:

avrdude: Device signature = 0x000000 (retrying)
avrdude: Device signature = 0x000000 (retrying)
avrdude: Device signature = 0x000000
avrdude: Yikes! Invalid device signature.

But I accidentally found out that if I connect the arudino nano to the FTDI programmer just a second after running the command, it does get a correct ATmega328P signature and continues (ever if expected a different signature, by the way..)

anyone has an idea how to solve this?
Thanks!