I suspect they may be adulterated with "something". Try dissolving them in denatured alcohol, mentholated spirits or isopropanol and then evaporating the alcohol off. Any other "stuff" may separate from the shellac. The flakes may be intended for french polishing, in which case the "stuff" may be some form of wax, which typically would not dissolve in alcohol.
I don't have any experience with shellac bought in flake form but I am curious what would happen if you reconstituted them into a big mass. Bunch all of them together and heat them up. If this is successful perhaps the shellac can be used after all.