"myschedule" doesn't give access to the Quick Add for security reasons. A lot of stuff is implied with the Event Categories, which the Quick Add relies on - if you'll notice those with myschedule also don't have access to event categories. If you want a user to have access to "Quick Add", then they'll need to at least have access to "schedule" in feature access.
That said, the bug with the "Sorry, you don't have access" is fixed.