It's the cross bolt safety. All it has to do is move over a hair and it makes the trigger useless.
I think they made the holes too big in the receiver.
I just wrapped some wire around mine so that the safety can not be applied. If I carry it I will leave the bolt locked back until ready to shoot.
I shoot rifles lefty, but if you are right handed you can keep your thumb on it when shooting and not have to do what I did.