Upload_speed not respected

Development Platforms
6

Looking build.py it uses:

myboard = mykeys["board"]
myuploadspeed = mykeys["upload_speed"]
env.Replace(BOARD=myboard)
env.Replace(UPLOAD_SPEED=myuploadspeed)
print('\033[94m' + "Target board: " + myboard + " @ " + myuploadspeed + "bps" + '\033[0m')
Upload filesystem error "The chip stopped responding"