Well- if double tapping the date is the way it's supposed to be, then that sucks. I don't want to tap twice to open a date....
Strange when I used my thumb (which I seldom use in calendar) it required a double tap. When I tap using a forefinger single tap was only required.For me it only opens when I don't use my thumb. Not sure why.
I've had that issue with the 4s during the beta program, then with the 5s with iOS 9.0 Final but not with the 6 Plus with iOS 9.0 or 9.0.1. Neither does my wife's 6s with 9.0.1. It's 2:2 for us
All three were restored from the same backup so this most likely won't be causing this issue, either.
I think it's a 9.0.1 thing. I downgraded from 9.1 PB2 and now double tapping is the norm ...