During the maintenance phase, configuration management takes on the new challenge of supporting various code bases in use. In a perfect world, everybody would have the same version of the software, but it's impossible to get everybody to apply all the patches, and it's impossible to get everyone to upgrade.
The configuration manager has to come up with a set of policies and practices to coordinate the efforts of the maintainers, while simultaneously assuring that you can debug outdated but installed versions of the software.
We've examined a few of those procedures here. There are still challenges to examine:
What if two maintainers must modify the same file at the same time?
How do you ensure that the bugs actually get fixed?
How do you balance new development with maintenance?
How do you make sure that new bug fixes don't cause more problems than they solve?
We'll try to answer some of these questions in the next few months.