`latest` dist tag does not point back to the old version of npm packages

Steps to reproduce:

1: install two versions of a package and move it to a local npm repo (I used grunt)
2: with npm set up, do: npm dist-tag add grunt@1.0.1 latest
+latest: grunt@1.0.1
3: see that the latest tag is still 1.0.2: npm dist-tag ls grunt
latest: 1.0.2

The latest tag is never updated, even though the metadata is updated apparently:

2018-03-03 00:00:29,194 [http-nio-8081-exec-17] [INFO ] (o.j.r.n.r.h.AbstractNpmRepoHandler:164) - Updating npm package metadata '.npm/grunt/package.json' into repo 'npm-local'

Tagging seems to work for tags that aren't latest though:

npm dist-tag add grunt@1.0.1 testtag
npm dist-tag ls grunt
latest: 1.0.2
testtag: 1.0.1