Servo tiltmotor assignment works, but left/right tiltmotor wont

hi all,
i have my quadplane vtol working, with front tilting rotors. their servos have the generic tiltmotor assignment (i use QGC, don’t remember actual numeric value, will check) but if i assign the proper lefttiltmotor and righttiltmotor they stop to work (tilting). i use the mfe 4.1 fw based on 4.1 master dated end of 2020. is it normal or a bug?