If the index provided to the <prize> token is too large, you'll get the last prize in the prize list. For example, if you have 3 prizes, and you provide an index of 5, you'll get prize 3.
If you provide an index that is non-numeric, it will default to 1 (the first prize in the list).
So what you are seeing is in fact the intended behavior. You've asked it to display prize number 3, but there's only 1 prize, so it displays prize 1 instead.
I can add an option to display nothing if the index is invalid.