first thing, toss the new box back at the guy in the store. second, get a new chrome one like some one suggested. three, clean the grounding surfaces and the edges of the box.
at first I had a huge laugh at you post title and thought well that's correct it does happen when you turn the ignition off.
look down it the large plastic piece in the bottom pic and you will see those peskey little points on the spades in the e-bay link sticking into it. get something the...
this seems like a great idea. cut pieces out of the biggest areas in the shroud and install a small hinge or two on the top of the pieces so the swing open at speed.
check and make sure the plug wires are correctly installed. if your msd box has a rev limit plug in, use a higher rpm one. what valve springs are you using?