Simply pushing an image to a V2 repo would fail if the pushing user does not have delete permissions. This is due to the migration of the blobs from the _uploads directory to their final destination. The docker client shows:
Error pushing to registry: Server error: 403 trying to push mytag blob - sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
The access.log shows:
2015-08-11 21:11:27,925 [DENIED DELETE] docker-local-v2:mytag/uploads/sha256_a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4 for uriah/127.0.0.1.