When a package transfers ownership or is removed/re-added, it's not possible to republish the same version as one that has previously existed.
Of course, this doesn't save you if you're installing `^1.0.0`, the maintainer deletes the package, and someone else uploads a malicous `1.0.1`.
The package.json should allow pinning publisher usernames and optionally public keys, and shrinkwrap should pin hashes, not just versions.
EDIT:
Seems like it's impossible to re-upload X1.0, which fix this issue. I thought once a package was unpublished, it was possible to republish the exact same version.