Adding `track` or `defaultSort` to any List breaks admin UI

Any ideas whatsoever would be great.

Expected behavior

I should be able to instantiate a new List with track or defaultSort set without an issue.

Actual/Current behavior

But for some reason, I get the following error on the /keystone/signin page:

signin.js:978 Uncaught TypeError: $export is not a function
    at Object.76../_descriptors (signin.js:978)
    at s (signin.js:1)
    at signin.js:1
    at Object.15.../../modules/_core (signin.js:83)
    at s (signin.js:1)
    at signin.js:1
    at Object.4.core-js/library/fn/object/define-property (signin.js:19)
    at s (signin.js:1)
    at signin.js:1
    at Object.48../_an-object (signin.js:610)

Steps to reproduce the actual/current behavior

Just add one of the aforementioned options to a List, old or new.

Environment

Software	Version
Keystone	4.0.0-beta.7
Node	8.9.1

Babel config:

{
  "presets": [
    ["env", {
      "targets": {
        "node": "current"
      }
    }],
    ["stage-0"]
  ],
  "plugins": [
    "transform-runtime",
    "import-glob"
  ]
}