This has been "fixed" in 0.49. Prior to that Test::More would always load threads.pm and share its internal data if possible to make things thread safe.

In 0.49 it was changed so Test::More would not load threads.pm for you. You had to do it in your test before loading Test::More. So this bug should no longer effect tests that do not use threads.

And if you have 10,000 thread-enabled tests, god help you. ;) Actually I've long planned a "no history" option to avoid using too much memory in very long testing situations, so watch for that, too.