In 2017 LTS versions, the “x” button to close the window next to the minimise and full screen buttons is missing on MacOS.

1. Open or create a new project in a 2017 LTS Unity version.
2. Try to close the editor window with the “x” button in the top left.

Expected Outcome: The “x” is visible, and when clicked, closes the editor window.
Actual Outcome: There is a grey circle in place of the “x” and clicking it does not close the editor window.

Reproducible in 2017.4.30f1 and 2017.4.31f1
No issue if you move forwards to 2018.1.0a1 or 2018.4.8f1

License type: Pro