Has anybody noticed a reoccurring residue on their cups? I have a Diva, and when I'm not using it I notice that it gets this film on it that feels greasy. I wash it, boil it, and soak it in peroxide, and it seems squeaky clean, but soon afterward it feels gross again. I'm not worried enough to stop using it, and it's never caused me any problems, I'm just curious. I hope it's not degrading or something. I doubt it's bacteria, I haven't had any infections and I live in Phoenix, Arizona, not an environment that encourages bacteria growth. Or maybe I'm just imagining things?