ArduCopter enters RTL when sending SET_POSITION_TARGET_GLOBAL_INT

When sending the message SET_POSITION_TARGET_GLOBAL_INT from Python to ArduCopter, in guided or auto mode, RTL is engaged. Typemask set to 0xffff, so nothing should happen. sysID and component ID are both set to 0. I guess the message would just be ignored if something isn’t correct, but it engages RTL. What could be the reasons that RTL is engaged?

Maybe a bug. Please retest in Copter 4.0.4 SITL