I know that Revival Herb, Energy Root, and the other herbal remidies are suposed to be disliked by Pokemon as they are very bitter, thus liking their trainer less if they are healed with them. Is this still the case if they like bitter food?
Even though it's been a while since this question was asked, I found the answer. The bitter items DO lower happiness even if your pokemon likes bitter food.
http://bulbapedia.bulbagarden.net/wiki/Energy_Root
