/usr/lib/rpm/cpanflute creates a .spec file with "Group: Applications/CPAN". However according to /usr/share/doc/rpm-4.0.3/GROUPS this is not a valid group. Among other things, this creates problems when a cpanflute-based package is checked for validity by some system that insists on having a "legal" group (such as, for example, http://rhcontrib.bero.org/ ).
So edit cpanflute. The fix -- if necessary -- will be to remove cpanflute from rpm, as it's usefulness has come and gone.
By why not change cpanflute so that future releases of rpm-build do not have this problem?
Because the value of the Group: field that should be used is a Red Hat distro problem, not an rpm problem, and so cannot be solved in rpm source code.