OK, if I was told 2H is, and was described as natural, and partner jumped out of the blue to 4S, I would pass because 1) I don't what partner is doing, and 2) I really don't see that 5D/H is likely to be any better. It isn't as though one of the opponents has bid spades. If partner think's he's raising my spades, then that might make it more likely for me to try something else (5D and a wing and a prayer I guess). Therefore, I think that passing is an LA.