I don't know if this is a bug or a feature, but it seems to me that if spark can't traverse a single layer of insulation, that it shouldn't be able to toggle/trigger powered materials on the other side either.
it's easy enough to work around by just adding another layer of empty space between any powered particle you don't want activated and a potential activation source, but it's annoying and inconsistent.
I have an example in ID 1935674, but it's easy enough to replicate and I can't imagine I'm the first to notice it.