Stéphane Appercel I am trying to create a reproducer but it works for me. I am not using SE but standard Weld in embedded container one, but that shouldn't matter.
You can take a peek at the reproducer I tried here (last commit).
Maybe some of your classes have more complex hierarchy? Inherit some of the observer methods from abstract superclasses etc?

What's the difference between your second class (crashing) and third class (working) - could you post the class declarations? (E.g. public class Foo extends Bar<T>)

Also forgot to ask, does your problem appear with JDK 9 only? Or JDK 8 as well?