Two things:

1. There is a new version of Devel::Cover out on the CPAN, version 0.47, so maybe upgrading your module will fix your problems.
2. Also, from the pod:

   Perl 5.8.0 and 5.8.1 will give slightly different results to more recent versions due to changes in the op tree.

   So, that might be part of your problem. Perl 5.8.0 actually is kind of old, it was released over 2 years ago. Perl 5.8.5 is the latest version.