Ex:

• Project B is depending on artifacts from Project A.
• Builds for Project A and Project B are both triggered at the same time.
• The build of project A finishes earlier, so that Project A deploys its artifacts while Project B is still building (replacing the previous artifacts).

What can happen is that the build of Project B suddenly breaks, because it needs an artifact of Project A for which it already resolved the dependency, but yet of a different type. Maven is writing the local metadata file when resolving the pair groupId:artifactId of the first type, and is reading the same metadata file when resolving the same pair of the second type (which may come later in the build).

Actually I think that groupId:artifactId:type should be considered for the uniqueness of artifacts instead of groupId:artifactId, and this information be contained in the local metadata files.