Suppose team A has built a module M, which is used by many of the products of A. Team B borrows M from A. While using it, they find a bug in M. In that process, they also create a fix which works for them. The question is: What should be the process by which the bug is reported to team A, and how should the fix be incorporated?
The potential difficulty is that there are many products that A had made which use M. Hence, if the fix is incorporated in the next version, all those products need to be regression tested.
Of course, it's a very common problem, and people must be doing something to solve it at their own level. Can we note down some common-sense technique here?
