If you set up an OAuth 2 service and enable Authenticate token requests via HTTP headers then you cannot turn this off again.

To reproduce this issue

1. Go to Site administration > Server > OAuth 2 Services.
2. Click Custom to create a new custom service.
3. Enter:
   1. Name: test
   2. Client ID: test
   3. Client secret: test
   4. Authenticate token requests via HTTP headers: Yes
4. Click Save changes.
5. Click the edit (gear wheel) icon for the service.
6. Uncheck Authenticate token requests via HTTP headers and click Save changes.
7. Click the edit (gear wheel) icon for the service.

Expected results

Authenticate token requests via HTTP headers is no longer checked.

Actual results

Authenticate token requests via HTTP headers is still checked.