That is why you have to keep breeding back to silkies and refining and fine tuning. According to the SOP, type makes the breed. Chickens do not have pedigrees (although most breeders keep records); if the bird meets the standard, it IS the breed or variety. That said, you really want it to produce offspring with the same or better type and where the variety is predictable, and getting htere is part of the fine tuning.
When you are dealing with dominant genes, you can get a very good looking bird in the first cross, but the second generation will throw a lot of oddballs as all the other genes start pairing up in ways you did not even imagine. The farther you are into generations, the more of those oddball genes you can lose and get closer and closer to getting it right.