Got alerted to this by tweet - also a post on the moodle.org forums.

If you're using a Mac, please check whether you can open the "Insert equation" button (DragMath). Mac users are getting a blank screen such as seen here.

Seems to be no problem on Ubuntu and on Windows.

Mac users - please check; report on which OS version and what your Java update is.

(Also, any workarounds for getting equations in?)