Valve cover bolts backing out

[forestb]

Is it normal for valve cover bolts to back out? I have a set of aluminum valve covers on my SB 350. They started leaking and I was going to get a new set of fel pro cork gaskets. Before doing so on a hunch I checked to see if the bolts were loose. They were vary loose. One was so loose that I could tighten it with my fingers. They are threaded studs with nuts. I tightened them down tight but not too tight. Is this normal? I have heard of header bolts backing out but not valve cover bolts.