Optimizer sometimes use "index" instead of "range" access for UPDATE where PK IN (small list of values)

CREATE TABLE `t` (

`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,

`action` enum('update','create','delete','query') NOT NULL,

`status` enum('unclaimed','claimed','error','completed','paused','cancelled','exemptable','violation','blocked') NOT NULL,

... more columns here ...

`last_change` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,

`error_message` text CHARACTER SET utf8,

`partition_key` int(11) NOT NULL DEFAULT '0',

PRIMARY KEY (`id`),

... more multiple-column indexes here ...

) ENGINE=InnoDB AUTO_INCREMENT=3184963639 DEFAULT CHARSET=latin1

select * from information_schema.tables where TABLE_SCHEMA='test' and TABLE_NAME = 't'\G

*************************** 1. row ***************************

TABLE_CATALOG: def

TABLE_SCHEMA: test

TABLE_NAME: t

TABLE_TYPE: BASE TABLE

ENGINE: InnoDB

VERSION: 10

ROW_FORMAT: Compact

TABLE_ROWS: 271226130

AVG_ROW_LENGTH: 227

DATA_LENGTH: 61576822784

MAX_DATA_LENGTH: 0

INDEX_LENGTH: 93808164864

DATA_FREE: 27502051328

AUTO_INCREMENT: 3184963639

CREATE_TIME: 2016-08-05 13:08:55

UPDATE_TIME: NULL

CHECK_TIME: NULL

TABLE_COLLATION: latin1_swedish_ci

CHECKSUM: NULL

CREATE_OPTIONS:

TABLE_COMMENT:

1 row in set (0.00 sec)

mysql> EXPLAIN UPDATE test.t SET status = 'claimed' WHERE id IN (3191531520, 3191531548, 3191675779, 3191675794, 3191849444, 3191879324, 3192120630, 3192120649, 3192120666, 3192120681, 3192120694, 3192120710, 3192120722, 3192120732, 3192120742, 3192120754, 3192120765, 3192152806, 3192177807, 3192252972, 3192284688, 3192284434, 3192284713, 3192284461, 3192284485, 3192284748, 3192284506, 3192284763, 3192284777, 3192284528, 3192284790, 3192284556, 3192284574, 3192284590, 3192284615, 3192284368, 3192284634, 3192284383, 3192284651, 3192284400, 3192284415, 3192284671, 3192440124, 3192570421, 3192570439, 3192570456, 3192570471, 3192570487)\G

*************************** 1. row ***************************

id: 1

select_type: SIMPLE

table: t

type: range

possible_keys: PRIMARY

key: PRIMARY

key_len: 8

ref: NULL

rows: 48

Extra: Using where

1 row in set (0.00 sec)

2339259 system user test Connect 2594 updating UPDATE t SET status = 'claimed' WHERE id IN (3191531520, 3191531548, 3191675779, 3191675794, 3191849444, 3191879324, 3192120630, 3192120649, 3192120666, 3192120681, 3192120694, 3192120710, 3192120722, 3192120732, 3192120742, 3192120754, 3192120765, 3192152806, 3192177807, 3192252972, 3192284688, 3192284434, 3192284713, 3192284461, 3192284485, 3192284748, 3192284506, 3192284763, 3192284777, 3192284528, 3192284790, 3192284556, 3192284574, 3192284590, 3192284615, 3192284368, 3192284634, 3192284383, 3192284651, 3192284400, 3192284415, 3192284671, 3192440124, 3192570421, 3192570439, 3192570456, 3192570471, 3192570487) 0.000

mysql> SHOW EXPLAIN FOR 2339259\G

*************************** 1. row ***************************

id: 1

select_type: SIMPLE

table: t

type: index

possible_keys: PRIMARY

key: PRIMARY

key_len: 8

ref: NULL

rows: 1

Extra: Using where

1 row in set, 1 warning (0.01 sec)