No object disappears when Railtron is created, which is not the case for any other Robotron.
During Zoey's unmorphed fight against the Tronics, one of the Tronics' headpieces is moved up, briefly revealing the stunt actor underneath.
Even though The lights that serve as Jax's eyes are on all the time and flash when he talks but they are not on in the scene when he is used as robotron bait and nobody in the show seems to notice.
The camera crew is visible in Devon's motorcycle helmet visor.