d8s pull && d8s push doesn't work

[imjasonh]

$ bazel run cmd/d8s:d8s -- pull ubuntu $PWD/ubuntu.tar.gz
2018/04/23 12:50:07 Pulling index.docker.io/library/ubuntu:latest
$ ls -lh ubuntu.tar.gz 
-rw-r--r-- 1 redacted redacted 42M Apr 23 12:50 ubuntu.tar.gz
$ bazel run cmd/d8s:d8s -- push $PWD/ubuntu.tar.gz gcr.io/some-project/ubuntu:d8s
2018/04/23 12:52:07 Pushing gcr.io/some-project/ubuntu:d8s
2018/04/23 12:52:10 mounted sha256:817da545be2ba4bac8f6b4da584bca0fb4844938ecc462b9feab1001b5df7405
2018/04/23 12:52:10 mounted sha256:a9b30c108bda615dc10e402f62d712f413214ea92c7ec4354cd1cc0f3450bc58
2018/04/23 12:52:10 mounted sha256:67de21feec183fcd009a5eddc4de8c346ee0f4369a20047f1a302a90716fc741
2018/04/23 12:52:10 mounted sha256:d967c497ce230b63996a7b1fc6ec95b741aea9348118d3328c676f13be789fa7
2018/04/23 12:52:10 mounted sha256:d3938036b19cfa369e1081a6776b07b54be9612bc4c8fed7f139370c8142b79f
2018/04/23 12:52:10 blob sha256:739f09eca6e43d4e99d63fa442d2daeefc3fc1dc46b13ec5a1414de74a2b7c86 not found

This happens for images:

• pulled from gcr.io/aaa/foo and pushed to gcr.io/bbb/foo, and
• pulled from gcr.io/aaa/foo and pushed to gcr.io/aaa/bar

...so it doesn't seem to be correlated to cross-registry or cross-repository pushes.