Daniel A. Twogood, D.C. said:
>Basically, there are three main milk proteins: casein, lactoalbumin
>and lactoglobulin. Whey contains the latter two and is casein free.
>snip...
 
I think that agricultural processes to separate casein and whey components
of milk are not 100% complete.  The possibility of cross contamination is
very real.  It is a stretch to think that a whey ingredient would not
contain any casein.