This was a huge pain in the neck. The rise of Moo/se has helped somewhat.

Back in the day there was that horrible trend of using "inside out" objects that would let you reliably subclass something without knowing it's underlying module system.

Ovid's Cor project has some really great work on specifying a default OO sytem for Perl 5 (or maybe 7). https://github.com/Ovid/Cor/wiki