The CPAN-testers test with dev release of perl for two reasons. Yes, one is to find bugs in perl before official releases. However, we also do it so that module authors get advance notice of changes that will affect their code when the next version of perl is released. Judging by what
says, this change is deliberate, and the failure is because of a bugfix in perl where you were inadvertently relying on the old buggy behaviour.