CMD is right. This discussion is going on since iOS 7. Probably the first version that started throwing away touch input from the user in certain areas. If you're interested, last year Omni Group Lead UI designer explained the phenomenon in a detailed post at
http://metalbat.com/post/visible-ui-had-better-respond-to-input-right-away/. He also made a Youtube comparison:
I have the feeling, that Apple constantly tweaks this behavior. It was a bit better with last version of iOS 8 (8.4.1) and reached imo another low with iOS 9. But it can't really trace the whole input change, because there is no proper documentation in the release notes or the dev center. I don't know if there are to many users complaints about unintended input, or if this a metal rendering or battery management problem. But it affects my day to day usage in a negative way. When i noticed it for the first time noticed with the new 5S, i thought my display was broken. By now i have adapted to the new way, but i still don't like it.