[MaybiusStrip]

This is my nightmare. Implicit division of duties are natural, but they should definitely be combated. Otherwise, things fall apart when people go on vacation, or worse, leave the team.

The way to do that is to have a communal backlog of work that people pick up tasks from, and to have an on-call rotation. Both of those things are rudimentary software engineering best practices nowadays. No one should be quietly maintaining things in their own corner. Situations like the ones described in the original post should be made part of on-call duties, or, even better, automated away.