This seems to be only an issue currently with the 13 nightlies, no problems in 12.
Add gradebook tool to a site. On the Settings page, Grade Entry, clicking "Percentages" and Saving doesn't do anything. The value stays on "Points" and a message comes up saying that "The settings were successfully updated".
It looks like saving other settings works and I don't see any error messages. It works when logged on as admin but doesn't work out of the box as an instructor account in a course site.