I was going to post what Theo did concerning the open bolt. I don't understand how it could be possible in an open bolt gun.
The only way I see it happening is if other parts of the gun were heating up to the point where they failed. Was something expanding to the point where the bolt could ride over a sear that would function in a cold gun? After it cooled the gun returned to functioning? That seems extreme, but I guess it might be possible especially considering claims they tore themselves entirely apart.