The "most problematic" module regarding its API was LWP::UserAgent, an indirect prerequisite (through WWW::Mechanize) for WWW::Mechanize::Shell. At a certain version, WWW::Mechanize monkeypatched LWP::UserAgent to provide credentials, and at another version, LWP::UserAgent changed its scheme so that the monkeypatch changed the wrong routine. WWW::Mechanize didn't specify the LWP version number until a later release, so after some trial and error, I pulled up the prerequisite version number of WWW::Mechanize to fix that.

This was a one time thing so far, so I haven't felt it a real nuisance.