Ha! I didn't realize that was even a bug. My first vamp (acquired random NPC) came with the stomach trait and I assumed it meant "all" food, even plasma. I had this mental image that Sim vampire fangs fed directly into the circulatory system so the traits meant the usual medical order of "nothing by mouth" or absorbed through intestines. Strict absorption via .. fang?
But, it looks like it is a bug! Amusingly I already had her make the drink to respec since she was, of all things, a foodie too. Ironically she fed of her mother-in-law to be who her fiance still lives with. But *only* after she became pregnant. The things some Sim grandmothers will do for grandchildren!