Frustrations with CalDAV tasks

I tried to use CalDAV tasks again. It did not go well. The problem with CalDAV tasks is often that every client only implements a portion of the massive spec. Sure, makes sense, nobody wants to implement all the stuff it has. But then you try to use different apps with it, and they all expect different things for such simple thing as marking a task done. For example, one app can mark task 100% done, but it doesn't set its status as "COMPLETED". Then other app does not care about the 100% don...