Oh, but they're working on it, they said. Great. Maybe they'll have it ready for the launch of iOS 10.
Another thing that's just plain stupid is how Wunderlist handles due date notifications and reminders. In addition to the built-in notifications of iOS and OS X, Wunderlist also has an "Activity" view which shows a big red badge if there's a new notification. So you have to open this view in order to clear it - on every single device you use Wunderlist with. And even if you actually tick off the respective item, the badge is not removed. You still have to clear it by yourself. Additionally, checking an item does not clear its notifications either. So you also have to manually discard all notifications, again on all devices you use Wunderlist with.
It's just shit. Time to find another ToDo app. (Not just for these two reasons, of course.)