create a project with groupId=abc and 10 tests. Build. It will score 11 due to ten new tests.
Now change the groupId=xyz, build again. It will score 11 again, treating the existing 10 tests as new, because jenkins records the tests under the groupId/artifactId.
It should probably say 10 tests removed or disabled under abc = -10, and 10 tests added under xyz =+10, so net off as zero. Or just ignore group and artifact ids when counting tests.