I have experienced this, as well, but I think it was just a fluke. I tested this again with a pack of shrimp and some cookies, and I get a bunch of rep gain. However, normally, you get about like... 0.50 or so a cookie? My point is, it's a low number. I added shrimp, and one of the rep gains were around 1.50 or so. That being said, I think they still get rep from shrimp, but maybe the popup doesn't appear sometimes.