This wasn't just any module, it is in the perl core.

I didn't expect perl 5.8 to have binary compatibility with perl 5.6.X.

One of the challenges with testing is trying things on the many different versions of systems. Imagine CPAN test results as a table, where the rows of the table are the modules, and the columns of the table are all the possible configurations of perl, I think that only a very small percentage of the table is filled in. It's a really great project and I hope that the table continues to become more filled-in.

Yet I'm not sure that the cpan testers would have found this particular problem with an automated CPAN testing process. The module passed its tests. It just broke perl when I installed it. In a response to chromatic's node below, I have included more details about what happened.

I don't expect every module to be backwards compatible. But if a pure perl module is in the core, and passes its tests, I don't expect it to break perl itself when it is installed. For the most part, my expectation has been met. I think that there is a big challenge to make a transition such as 5.6.0/1 to 5.6.8 work smoothly, and perhaps some modules have trouble with this.

It should work perfectly the first time! - toma