I toe punched all the chicks, so that I knew they were carrying white. I crossed a blue cockerel on my white hens. I got blue, black and splash chicks. I only kept a splash and blue pullet.
And yes, this generation I am getting some blue and black chicks. Unless you take the dark bird out of the white pen, you will continue to get b/b/s chicks carrying recessive white out of your white pen.
I don't recommend using white in the b/b/s pen.
What you are referring to doesn't make any sense to me and the whites may have been carrying something weird beneath the white. With recessive white if both parent birds are white all the offspring should be white. The only leakage I have ever seen on a recessive white is a bit of red or some feathers with peppering on them no spots.