Bug #74962 Matching in char field type is not correct

Description:
1) create table 
CREATE TABLE IF NOT EXISTS `in_docs` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `doc_type` smallint(6) NOT NULL DEFAULT '0',
  `sender_code` varchar(10) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
  `orig_reg_number` varchar(25) COLLATE utf8_unicode_ci NOT NULL,
  `orig_sent_date` date DEFAULT NULL,
  `followup_doc_id` int(11) NOT NULL,
  `reg_year` char(2) COLLATE utf8_unicode_ci NOT NULL,
  `reg_number` int(11) NOT NULL,
  `paper_reg_number` varchar(25) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
  `title` text COLLATE utf8_unicode_ci NOT NULL,
  `contact_id` int(11) NOT NULL DEFAULT '0',
  `contact_info` varchar(255) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
  `reg_date` date NOT NULL DEFAULT '0000-00-00',
  `deadline` date DEFAULT NULL,
  `ext_response_status` enum('none','accept','reject') COLLATE utf8_unicode_ci NOT NULL DEFAULT 'none',
  `deadline_notes` varchar(255) COLLATE utf8_unicode_ci NOT NULL DEFAULT '',
  `creator_user_id` smallint(11) NOT NULL DEFAULT '0',
  `access_level_id` smallint(6) NOT NULL DEFAULT '0',
  `fully_electronic` tinyint(1) NOT NULL DEFAULT '0',
  `media_type_id` smallint(6) NOT NULL DEFAULT '0',
  `modified` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  `created` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
  PRIMARY KEY (`id`),
  UNIQUE KEY `reg_year_and_number` (`reg_year`,`reg_number`),
  KEY `reg_date` (`reg_date`),
  KEY `orig_reg_number` (`orig_reg_number`),
  KEY `contact_info` (`contact_info`),
  KEY `title` (`title`(333)),
  KEY `followup_doc_id` (`followup_doc_id`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci PACK_KEYS=0 COMMENT='Incoming Documents' AUTO_INCREMENT=31824 ;

2) Then import data
INSERT INTO `in_docs` (`reg_year`, `id`, `reg_number`) VALUES
('11', 31659, 33),
('11', 31660, 34),
('11', 31657, 31),
('11', 31658, 32),
('11', 31656, 30),
('11', 31655, 29),
('11', 31654, 28),
('11', 31652, 26),
('11', 31653, 27),
('11', 31651, 25),
('11', 31650, 24),
('11', 31649, 23),
('11', 31648, 22),
('11', 31647, 21),
('11', 31646, 20),
('11', 31645, 19),
('11', 31644, 18),
('11', 31643, 17),
('11', 31642, 16),
('11', 31640, 14),
('11', 31641, 15),
('11', 31639, 13),
('11', 31638, 12),
('11', 31637, 11),
('11', 31636, 10),
('11', 31635, 9),
('11', 31634, 8),
('11', 31633, 7),
('11', 31632, 6),
('11', 31630, 4),
('11', 31631, 5),
('11', 31629, 3),
('11', 31627, 1),
('11', 31628, 2),
('12', 31661, 1),
('12', 31662, 2),
('12', 31663, 3),
('12', 31664, 4),
('12', 31665, 5),
('12', 31666, 6),
('12', 31667, 7),
('12', 31668, 8),
('12', 31669, 9),
('12', 31670, 10),
('12', 31671, 11),
('12', 31672, 12),
('12', 31673, 13),
('12', 31674, 14),
('12', 31675, 15),
('12', 31676, 16),
('12', 31677, 17),
('12', 31678, 18),
('12', 31679, 19),
('12', 31680, 20),
('12', 31681, 21),
('12', 31682, 22),
('12', 31683, 23),
('12', 31684, 24),
('12', 31685, 25),
('12', 31686, 26),
('12', 31687, 27),
('12', 31688, 28),
('12', 31689, 29),
('12', 31690, 30),
('12', 31691, 31),
('12', 31692, 32),
('12', 31693, 33),
('12', 31694, 34),
('13', 31695, 15),
('13', 31696, 1235),
('13', 31697, 1236),
('13', 31698, 1237),
('13', 31699, 1238),
('13', 31700, 1239),
('13', 31701, 1240),
('13', 31702, 1241),
('13', 31703, 1242),
('13', 31704, 1243),
('13', 31705, 1244),
('13', 31706, 1245),
('13', 31707, 1246),
('13', 31708, 1247),
('13', 31709, 1248),
('13', 31710, 1249),
('13', 31711, 1250),
('13', 31712, 1251),
('13', 31713, 1252),
('13', 31714, 1253),
('13', 31715, 1254),
('13', 31716, 1255),
('13', 31717, 1256),
('13', 31718, 1257),
('13', 31719, 1258),
('13', 31720, 1259),
('13', 31721, 1260),
('13', 31722, 1261),
('13', 31723, 1262),
('13', 31724, 1263),
('13', 31725, 1264),
('13', 31726, 1265),
('13', 31727, 1266),
('13', 31728, 1267),
('13', 31729, 1268),
('13', 31730, 1269),
('13', 31731, 1270),
('13', 31732, 1271),
('13', 31733, 1272),
('13', 31734, 1273),
('13', 31735, 1274),
('13', 31736, 1275),
('13', 31737, 1276),
('13', 31738, 1277),
('13', 31739, 1278),
('13', 31740, 1279),
('13', 31741, 1280),
('13', 31742, 1281),
('13', 31743, 1282),
('13', 31744, 1283),
('13', 31745, 1284),
('13', 31746, 1285),
('13', 31747, 1286),
('13', 31748, 1287),
('13', 31749, 1288),
('13', 31750, 1289),
('13', 31751, 1290),
('13', 31752, 1291),
('13', 31753, 1292),
('13', 31754, 1293),
('13', 31755, 1294),
('13', 31756, 1295),
('13', 31757, 1296),
('13', 31758, 1297),
('13', 31759, 1298),
('13', 31760, 1299),
('13', 31761, 1300),
('13', 31762, 1301),
('13', 31763, 1302),
('13', 31764, 1303),
('13', 31765, 1304),
('13', 31766, 1305),
('13', 31767, 1306),
('13', 31768, 1307),
('13', 31769, 1308),
('13', 31770, 1309),
('13', 31771, 1310),
('13', 31772, 1311),
('13', 31773, 1312),
('13', 31774, 1313),
('13', 31775, 1314),
('13', 31776, 1315),
('13', 31777, 1316),
('13', 31778, 1317),
('13', 31779, 1318),
('13', 31780, 1319),
('13', 31781, 1322),
('13', 31782, 1321),
('14', 31783, 1),
('14', 31784, 2),
('14', 31785, 3),
('14', 31786, 4),
('14', 31787, 5),
('14', 31788, 6),
('14', 31789, 7),
('14', 31790, 8),
('14', 31791, 9),
('14', 31792, 10),
('14', 31793, 11),
('14', 31794, 12),
('14', 31795, 13),
('14', 31796, 14),
('14', 31797, 15),
('14', 31798, 16),
('14', 31799, 17),
('14', 31800, 18),
('14', 31801, 19),
('14', 31802, 20),
('14', 31803, 21),
('14', 31804, 22),
('14', 31805, 23),
('14', 31806, 24),
('14', 31807, 25),
('14', 31808, 26),
('14', 31809, 27),
('14', 31810, 28),
('14', 31811, 29),
('14', 31812, 30),
('14', 31813, 31),
('14', 31814, 32),
('14', 31815, 33),
('14', 31816, 34),
('14', 31817, 35),
('14', 31818, 36),
('14', 31819, 37),
('14', 31820, 38),
('14', 31821, 39),
('14', 31822, 40),
('14', 31823, 41);
3) Then execute query
"SELECT IF(MAX(reg_number) <= 0, 1, MAX(reg_number) + 1) FROM in_docs WHERE reg_year='14-1'"
IT will return 42 but there are not row where reg_year="14-1" (in addition reg_year is char(2))

How to repeat:
See my description

-> ('14', 31823, 41);
Query OK, 197 rows affected, 3 warnings (0.02 sec)
Records: 197  Duplicates: 0  Warnings: 3

mysql 5.6 > SELECT IF(MAX(reg_number) <= 0, 1, MAX(reg_number) + 1) FROM in_docs WHERE reg_year='14-1';
+--------------------------------------------------+
| IF(MAX(reg_number) <= 0, 1, MAX(reg_number) + 1) |
+--------------------------------------------------+
|                                               42 |
+--------------------------------------------------+
1 row in set (0.00 sec)

mysql 5.6 > ALTER TABLE in_docs DROP INDEX `reg_year_and_number`;
Query OK, 197 rows affected (0.08 sec)
Records: 197  Duplicates: 0  Warnings: 0

mysql 5.6 > SELECT IF(MAX(reg_number) <= 0, 1, MAX(reg_number) + 1) FROM in_docs WHERE reg_year='14-1';
+--------------------------------------------------+
| IF(MAX(reg_number) <= 0, 1, MAX(reg_number) + 1) |
+--------------------------------------------------+
|                                             NULL |
+--------------------------------------------------+
1 row in set (0.00 sec)

mysql 5.6 > SHOW VARIABLES LIKE "%VERSION%";
+-------------------------+--------------------------------+
| Variable_name           | Value                          |
+-------------------------+--------------------------------+
| innodb_version          | 5.6.23                         |
| protocol_version        | 10                             |
| slave_type_conversions  |                                |
| version                 | 5.6.23                         |
| version_comment         | Source distribution revno 6246 |
| version_compile_machine | x86_64                         |
| version_compile_os      | Win64                          |
+-------------------------+--------------------------------+
7 rows in set (0.00 sec)

mysql 5.6 >

But there are not any row where you can find '14-1'.
Is it equal with (SELECT IF(MAX(reg_number) <= 0, 1, MAX(reg_number) + 1) FROM in_docs WHERE false;) ?

Thank you for the bug report.

But I want to know is it bug or just my wrong usage?
Thank you.