UI is blocked while any animation/transitions, taps and swipes are ignored
This is present overall in many interactions on the whole OS. While some animation is happening, even if I can already see the end result or if I know where I am navigating to, and I start swiping on tapping on the screen, the OS won't recognize until animation ends. At many times this "trows away" my input.
I will describe the whole flow in the "Steps to reproduce" but this two minute video will explain even better: https://www.youtube.com/watch?t=52&v=5Ti0KdXrgSE
Although the video is comparing iOS 8 to iOS 3, this is still true and reproducible on iOS 9 beta. The video also talks about multi-tasking and switching apps, but this issue is not asking to address this particular interaction, as it's out of scope (although is fair to assume that improvements can be made as a separate issue).
I can observe two groups of OSs that I can reproduce: