[bvw]

Consistent with theory by Freeper refermech that he posted yesterday morning:

It sounds like it is all coming out of the same container. As you get closer and closer to the bottom the product becomes finer and finer just like a box of cereal. Mystery solved!!

[6ppc]

I think refermech is right! Spooning it from a container while stuffing envelopes would avoid stirring it up.