The bitter after-taste of the Cranberries is probably due to the "puckering" astringency of the Cranberries.

With regard to your chilli question, I began thinking about the very same thing the other day. I had namely purchased chilli-chocolate. And for the first bites it has absolutely no burn whatsoever, but once the chocolate begins to melt, the burn sets in slowly. I hypothesize, and it would be a cool experiment to carry out... I think it is due to the fatty particles in the food that sequester the chilli burning ones, which only come to the fore once the fat has been cleared off the tongue or broken down by the lipases. Similarly I think if one didn't have an oily food, but instead the mixture were water based, the burn would probably be instantaneous??