Sounds like Apple's underinvestment in mobile Safari makes it currently impossible to implement this well in web pages in iOS, and that the AMP team is working with Apple to fix their broken platform. I don't see how this isn't Apple's bug.
I'm not sure it was a bug, it sounds like it was a design decision. Maybe not in GOOD one, but I doubt it was a true bug.
Apple's response indicates it was a bug, and nowhere has Apple said "this is a design decision we are now changing".