Wow, almost exactly the same thing has now happened twice when I seasoned a nickel-plated skillet.
I have gotten pretty good at seasoning non-plated pieces by now (heat at 450 degrees for 30 minutes, use a really really thin coat of Crisco applied with an old cotton t-shirt, wipe off the piece with paper towels before putting back in the oven, heat at 400 degrees for 30 minutes, leave in the oven until cool) and never get the steaks and spots EXCEPT for on this plated skillet.
I am wondering if the reason is that the plating makes the surface so smooth and "poreless" that the Crisco puddles up rather than sinks in. I am going to have to try again, but would love to hear back from anyone with more experience in seasoning plated pieces before I do.