SITL - issue with yaw command

Hi,

For 4 days I have issues with sending yaw command to a SITL multirotor.

A basic script that was working perfect before hand shows several bugs, and especially this one.
I am using mission planner 1.3.70 and SITL V4.0.4-dev.

The copter simply does not take in account the message :
msg = vehicle.message_factory.command_long_encode(
0, 0, # target system, target component
mavutil.mavlink.MAV_CMD_CONDITION_YAW, #command
0, #confirmation
heading, # param 1, yaw in degrees
0, # param 2, yaw speed deg/s
1, # param 3, direction -1 ccw, 1 cw
is_relative, # param 4, relative offset 1, absolute angle 0
0, 0, 0) # param 5 ~ 7 not used
# send command to vehicle
vehicle.send_mavlink(msg)

Is it a know issue ?

Thanks in advance