Currently in master, a new behavior is to log every command failure or assertion. This includes command parsing errors and every uassert that a command may throw. For example, the not-master assertion:

2015-06-18T13:47:18.401-0400 I COMMAND  [conn2] assertion while executing command 'getMore' on database 'test' with arguments '{ getMore: 62016858025, collection: "foo", term: 1 }' and metadata '{}': 13435 not master and slaveOk=false

I believe we should change this to log at debug log level 1, to avoid filling the server log with what are essentially user-generated common errors.