NPM: Git vs non-git dependencies

package.json

{
  "name": "npmgit",
  "version": "0.1.0",
  "description": "Show that git dependencies are reinstalled on every `npm install.",
  "dependencies": {
    "bunyan": "^1.3.4",
    "restify": "git+ssh://git@github.com:mcavage/node-restify.git#3.0.0"
  }
}

When running npm install, normal dependencies (here: bunyan) are installed just once. But git dependencies (here: restify) are reinstalled whenever npm install is executed.

Notice that both depend on dtrace-provider but only restify's copy is recompiled every time.