This doesn't happen anywhere near as often when

• You have a repository that records checkouts and checkins
• You have a sufficient set of regression tests that run periodically (at least once daily) against the repository
• You move from individual ownership of code to group ownership

Unless you have a repository, you're eventually toast. And any repository worth its salt will let you quickly tell who changed what, when, and will let you run a diff between different versions of a file (e.g., here's what so-and-so changed while I was gone).

If you don't have a sufficient set of regression tests that run automatically, breakage gets overlooked or hidden, and it's easier to pin the problem on someone else. To maximize peer pressure, the regression test suite can produce a web page listing modules that fail, showing also any recent checkins that might impact the failing module (and who made the checkin).

When the group owns the code, there's less opportunity for problems to be framed in terms of a dispute between two developers. Instead, it becomes an issue between the team and the miscreant developer.