I should have said so at the beginning, but Anonymonk is reminding me so I'll say that I've had similar experiences moving from perl 5.6.1 to perl 5.8.0 solving a number of problems I had integrating XML::Twig into this same project (that requirement then went away). So I'm now testing/developing/going into production with perl 5.8.6. It took us nearly a year to get them to upgrade to 5.8.6, I'm not going to be able to convince them to move up again for at least another year, possibly two.

However, at the very least, you should try it with these new versions. If you find that it works in one version but breaks in the previous version, then you have a much smaller area to examine for changes. It would probably be much easier to try to diff say, perl5.8.5 and perl 5.8.6 to see exactly what bug you've hit. Or possibly not.