My bad, I've now read the full release notes on TJC, the new pop-up dialog only appears when the other side ends the call, and I could get it to appear on my device. I misunderstood the feature and I was expecting to see it when I ended the call, too. I think it is actually a small neat feature to have, you just need to tap/scroll anywhere to make it go away, nothing too annoying (IMHO of course).