This is really about gimbal lock. A rotation like this
RotateEntity ent, 90, anything, anything
leaves the z-axis pointing directly down, where the negative y-axis used to be. Thus yaw and roll both turn around the same (vertical) axis.
RotateEntity ent, 90, anything, anything
leaves the z-axis pointing directly down, where the negative y-axis used to be. Thus yaw and roll both turn around the same (vertical) axis.