Yes I can reproduce it here. I think it may be related to how quickly you tap.
I noticed that when I quickly tap, the button will be pressed. But if I tap and hold for 400ms~ before I lift my finger, it won't work.
Safari on iOS blows - it is quite buggy. The same thing happens in Wordpress when you are using certain themes - the "Read More" button no longer functions properly. You tap on it and nothing happens. We have found that certain css styles break anchor tags on iOS Safari. Stupid, I know. To get the "Read More" button on our Wordpress working again on iOS we've had to disable some shadow css styling. Something similar is probably happening here.