1.8.4-SNAPSHOT < 1.8.4
This doesn't appear to be happening... the comparator strips off the "-SNAPSHOT" qualifier, but then ignores it entirely.
This is relevant because when loading modules, if it finds multiple modules with the same ID it chooses the "most recent" one and deletes the others from the file system.
So, for example, if you have the following two modules in your modules directory:
"somemodule-1.8.4-SNAPSHOT" will be started, and "somemodule-1.8.4" will be removed, when really you'd want to keep "somemodule-1.8.4" as it is the most recent version.
To reproduce, you can take the existing test:
and set the older version to "1.8.4-SNAPSHOT" and the newer version to "1.8.4".