You're probably looking at the prize screen wrong. You can win one of three prizes, and the one that flashes should be the one you get.
I've never had your problem before, so i'm mearly guessing it's an error on your part (no offense). However, if you can get some screenshots of this happening (like it shows tht you'd win a tranq, and in the next shot it says "recieved megaelixer", then maybe we can take a closer look at the problem