hey antonio, thanks for your detailed message - i didnt know that.
however, I flashed my rainbowduino v2 (using an atmega 328) fw at least 50times without any issues using:
-upload clean sketch to arduino
-connect rx+tx (other cables are always connected)
-upload rainbowduino fw
-disconnect cables
-upload arduino fw
what happens if you connect the reset line from the arduino with the rainbowduinos, isn’t that like a pass through? (like rx/tx)?
cheers
@miso: strange - I also use an mac book, without any issues…