Firing the event after a ProblemChange in the DefaultSolver is omitted to avoid publishing uninitialized solutions [1] - when the ProblemChange has been processed, but not even the CH phase ran. Instead, the CH phase fires the event when it finishes.

During the partitioned search, the CH phase does not fire the best solution event and thus, there are no events fired immediately after submitting a ProblemChange.

[1] https://github.com/kiegroup/optaplanner/commit/a5fe8bd7f4596ea6f4effa24689255e4dbae94f6