Why is broccoli-asset-rev fingerprinting my files differently on different servers?

I am getting different hashes running the same build process with the same package.json using the same git hash on different machines.

My build process that builds my dist is ember build --environment production.

When run locally, I get a fingerprint like: 61d20923c56bef5632711ada4bb76246.

When run on my CI server, I get a fingerprint like: c45ef7f3dbb98441099e10e59e09abef.

When run on my Heroku server, I get a fingerprint like: 0485d770eb6209fa1387242e0e889d5f.

This is a problem because I push my assets to S3 with grunt and then expect that fingerprint to be the same.

This same build process was working two weeks ago for me, so I can't imagine what changed.

I'm on npm 2.1.14, node 0.10.35, ember-cli 0.1.15 and broccoli-asset-rev ^2.0.0.