Could a short exhaust cause valve damage?

I have heard from a few people, not that I actually believe any of them, but it is worth checking with the experts, that you can cause valve damage if you use an exhaust system that is too short. I am planning on using Lakester style header on a SBC with no baffles. I want to make sure that if I do, it will not cause any damage to the motor. I also want get a definitive answer to this question. As always, any help is greatly appreciated.

Ran a 56 chevy with a 235 6 cylinder which we split the manifold and ran short pipes of about 3' with no problems except the cops didn't appreciate the noise.

Thechinspector hit the nail on the head. If you allow cold/ambiant air temp to get to a freshly scalded valve the fast cooling will crack/warp the valve. If you run at least a couple feet of header your all fine, I ran a pulling truck with a small rust hole in the primary just outside the flange and it went all summer. I would never start an engine I liked and run it hard with no manifolds/headers and shut it off, your asking for trouble. BTW, you would also be throwing flame out the ports a few inches if you ran open heads.

Thank you all for your input. It sounds like the lakester headers I am planning in running will be long enough to prevent cold air from getting near the valaves.