Thanks, that makes sense to me now. perldoc base:

'use base qw[Foo Bar]' is roughly equivalent to:
BEGIN {
    require Foo;
    require Bar;
    push @ISA, qw(Foo Bar);
}

...

If any of the base classes are not loaded yet, *base*
silently "require"s them.
[download]

It seems like quite a subtle bug to fall into - you can use @ISA directly to declare a subclass of Exporter and think you're getting an import method from the superclass, but actually because you haven't loaded Exporter, silently nothing will happen when you use the subpackage...

cheers
ViceRaid