Sometimes! I'm no chemist, but I recall reading here that there are several forms of Vit. C that are good for the body, but not so hot for developing.
My local health store sells a Vit. C powder that is good for me, but when mixed leaves a healthy amount of precipitate and doesn't do as good a job on film/paper that "proper forms" of Vit. C do. Others more knowledgeable in the specific names can fill us in.