It looks more and more like a bug to me.
One last check: could you try again but instead of reusing the same instance of detector to build two independent instances before passing them to the EventBasedScheduler constructors? Looking at the core, it should not change anything so I fear you will still get only one type of events. If you confirm this does not solve the problem, then please open a new issue at https://gitlab.orekit.org/orekit/orekit/issues. I consider this issue as important, so we will adress it very soon, before releasing upcoming 10.0.