River Runner, I think we are on the same wavelength.
As far as "fixing" the braintanning, I am using the term like they do in photography. When the image is first taken out of the developer it needs to be put into the "fixer" to make it permanent, otherwise the paper would continue to develop and turn the whole image black.
To really understand what the smoking does with buckskin, you have to understand the mechanics of braintanning a little bit. Braintanning can actually be done with several things besides brains as well. I have used egg yolks and a little neats foot oil for "brains". They key being that you need an emulsified oil. What the brains do is penetrate and lubricate the individual fibers of the hide. After soaking in the brains, the hide must be wrung out, and then "softened" as it dries. It must be stretched, abraided, etc. as it dries. Not constantly, but thoroughly periodically. What you are doing is keeping the fibers moving as it dries. If you just let it sit and dry out it will be a big potato chip (the hide has literally glued itself together).
Once the hide is dry and as soft as you want it (you can brain it again if it isn't quite as soft as you like), you smoke it. What the smoke does is actually get into the spaces between the fibers and the smoke molecules bind extremely well to the fibers, which is why you can't wash it out. These molecules take up the space that water would otherwise get into and make the hide glue that makes an unsmoked hide stiffen up. You can wash the color out by repeated washings, but the molecules that keep is soft can not be washed out. Once the soft hide is smoked, the brains (or tanning) being leached out is more or less irrelevent. The braining and softening process gets the hide soft, the smoking keeps it soft.
River Runner, you probably already know some of this, but I thought I would post it for the benefit of other as well.