Here's a hint as to why. Have a look at the output of
perl -Mversion -E "say qv('0.30')->numify(); say qv('0.3000')->numify();"
CPANPLUS uses Module::Load::Conditional, which uses version.pm to compare
versions and finds the installed Module::Build lacking.
The fix is to change line 18 in Module/Build.pm from
$VERSION = '0.30';
to
$VERSION = '0.3000';
