Running the latest Rhino 5 and Brazil Beta - but I have noticed this with older versions also:
When I use one of certain textures - it could be *any* texture, not sure yet -- that mix one or more other textures, and then I replace the top texture (the mix) with a different texture, the two or more sub-textures stay in the material's 'tree'.
So, for example, I create a Blend Texture, I put a Bitmap in one slot, and a Tile in the other. I apply that Blend to the color of a Brazil Basic or Advanced material. Then I later replace that Blend Texture with, say, a new Bitmap texture. The original Bitmap and Tile are still shown as sub-textures to that new Bitmap Texture.
I believe this caused a crash for me at one point (I was using the slightly earlier version of Brazil's Beta at the time), but now it's just an annoyance - there seems to be no way to purge these items from the tree, short of clearing that slot of the material completely.
Interestingly, when I undo (CTRL-Z) after clearing the texture slot, then the tree is repopulated correctly. So this really makes me think it's just a problem with the populating of that tree.
I'm attaching two screenshots: before and after