Now that use cases hide the actual method, deficiencies in their implementation have become critical. Basically, their whole body is based on the use case definition, so they show up as abstract (whether they are or not), attributes are lost (such as "final"), and the definition classes become useless.
To put it simply, the documentation for all methods with use cases is now BROKEN, in a way that goes way beyond simply displaying a false signature. And, of course, we presently have no way of actually looking up the real signature – since definition classes is broken, we can't even track the source code for it.
Personally, I consider this issue Critical. The nightly docs are used by a lot of people, but they mostly know how to get around. If, however, a release is made in the current condition, there will be hell to be paid because of these issues.