Same error here. Just updated from 4.2 to 4.2.2 but the error still exist. I can create new fields, but can’t update existing ones. I get a “xxx updated.” message, but the field doesn’t get updated.
The server logs don’t show any errors.
Also updated WP from 3.6 to 3.6.1 – no success.
Debug mode is active, too. Nothing.