Thread.pm cheats; it uses the functions in the threads package, but doesn't load threads.pm, instead just loading thread's XS component. This worked great...until the threads module was changed to have threads::new be just an alias to threads::create, with the alias being set in the .pm file, not via XS. And suddenly, if you load Thread but not threads, there is no threads::new function anymore.

I believe this is only a problem with the CPAN threads module at the moment. The workaround is to use threads;.