The glitch on the left side of the cable car is disallowed because it gives whoever is on the red side of it an unfair disadvantage, they can crouch behind it, line up their shot, quickly uncrouch, shoot and crouch back down, this doesn't give the blue side enough time to take a shot which is why that's disallowed.

The train glitch allows players both sides of the train to shoot from either side and if you've got tacs that's even better because you can see exactly where the enemy is, so in my opinion this is not an unfair advantage and is allowed in the server.