Copper and zinc release compounds that are toxic to all carnivorous plants. It's not just nepenthes.
Sarracenia Northwest has the info (somewhere).
Yep - here it is:
http://en.allexperts.com/q/Carnivorous- ... lant-1.htm
"As for the metal pot, if the pot is stainless steel it will be fine. If it's copper or zinc (galvanized) it will kill your plant. Those metals give off compounds toxic to carnivorous plants." - Jeff Dallas, Sarracenia Northwest
That's just for a pot. Zinc and copper in fertilizer is no good in any remotely-significant amount, as such. Like I said, though, people have used 0.5% copper/zinc fertilizer on Neps for years and none have died from it (that's been documented). It's the higher concentrations you don't want. I've seen great results from ferts that have small amounts of copper/zinc, like mine.
Miracle Gro products have no place in the CP world whatsoever. Not a single one of them.