Son of a gun. I'd like to thank pc88mxer and FunkyMonk for their accurate and helpful responses and extend a special thanks to Joost for answering the question I didn't ask: "Why doesn't my original version of this test script, with A and B in seperate pm files work?". The answer is, of course, when my original script did this:

#! /usr/bin/perl 
use strict;
use warnings;

use A;
use B;

A->new();
B->new();
[download]

the runtime was finding the standard package B and not my test package. Thanks again!