Bug #71206 GROUP_CONCAT changes GROUP BY behavior

Description:
Queries 

SELECT GROUP_CONCAT(`i_instanceid`), COUNT(*) FROM `test` GROUP BY `i_descriptions`

and 

SELECT COUNT(*) FROM `test` GROUP BY `i_descriptions`

produces different row count on certain data

How to repeat:
INSERT INTO `test` (`i_instanceid`, `i_descriptions`) VALUES
(1, '[{"type":"html","value":"\\u0425\\u043e\\u043b\\u043e\\u0434\\u0440\\u044b\\u0436\\u0435\\u0441\\u0442\\u0432\\u043e 2013","color":"99ccff"},{"type":"html","value":"<div style=\\"white-space: nowrap; margin: 10px\\"><div style=\\"white-space: nowrap; padding: 3px;\\"><div style=\\"width: 60px; height: 32px; vertical-align: top; display: inline-block;\\"><div style=\\"width: 48px; height: 32px; vertical-align: top; display: inline-block; border: 2px solid rgb(255, 255, 255);>\\"><div style=\\"position: absolute; width: 48px; height: 32px; vertical-align: top; display: inline-block; background-size: contain; background-image: url(http:\\/\\/cdn.dota2.com\\/apps\\/570\\/icons\\/econ\\/sockets\\/gem_stat.ea886ecaac62d6eb..."><\\/div><div style=\\"position: absolute; filter:alpha(opacity=90); -moz-opacity:0.9; -khtml-opacity: 0.9; opacity: 0.9; width: 48px; height: 32px; vertical-align: top; display: inline-block; background-size: contain; background-image: url(http:\\/\\/cdn.dota2.com\\/apps\\/570\\/)\\"><\\/div><\\/div><\\/div><div style=\\"vertical-align: top; display: inline-block; margin-left: 12px padding: 2px\\"><span style=\\"font-size: 18px; color: rgb(255, 255, 255)\\">\\u0423\\u043d\\u0438\\u0447\\u0442\\u043e\\u0436\\u0435\\u043d\\u043e \\u043a\\u0430\\u0437\\u0430\\u0440\\u043c: 0<\\/span><br><span style=\\"font-size: 12px\\">\\u0420\\u0443\\u043d\\u0430<\\/span><\\/div><\\/div><\\/div>"}]'),
(2, '[{"type":"html","value":"\\u0425\\u043e\\u043b\\u043e\\u0434\\u0440\\u044b\\u0436\\u0435\\u0441\\u0442\\u0432\\u043e 2013","color":"99ccff"},{"type":"html","value":"<div style=\\"white-space: nowrap; margin: 10px\\"><div style=\\"white-space: nowrap; padding: 3px;\\"><div style=\\"width: 60px; height: 32px; vertical-align: top; display: inline-block;\\"><div style=\\"width: 48px; height: 32px; vertical-align: top; display: inline-block; border: 2px solid rgb(255, 255, 255);>\\"><div style=\\"position: absolute; width: 48px; height: 32px; vertical-align: top; display: inline-block; background-size: contain; background-image: url(http:\\/\\/cdn.dota2.com\\/apps\\/570\\/icons\\/econ\\/sockets\\/gem_stat.ea886ecaac62d6eb..."><\\/div><div style=\\"position: absolute; filter:alpha(opacity=90); -moz-opacity:0.9; -khtml-opacity: 0.9; opacity: 0.9; width: 48px; height: 32px; vertical-align: top; display: inline-block; background-size: contain; background-image: url(http:\\/\\/cdn.dota2.com\\/apps\\/570\\/)\\"><\\/div><\\/div><\\/div><div style=\\"vertical-align: top; display: inline-block; margin-left: 12px padding: 2px\\"><span style=\\"font-size: 18px; color: rgb(255, 255, 255)\\">\\u0423\\u0431\\u0438\\u0439\\u0441\\u0442\\u0432: 0<\\/span><br><span style=\\"font-size: 12px\\">\\u0420\\u0443\\u043d\\u0430<\\/span><\\/div><\\/div><\\/div>"}]');

CREATE TABLE IF NOT EXISTS `test` (
  `i_instanceid` int(10) unsigned NOT NULL,
  `i_descriptions` text NOT NULL,
  PRIMARY KEY (`i_instanceid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

This is also repeatable with latest and greatest 5.6.15:

C:\Program Files\MySQL\MySQL Server 5.6\bin>mysql -uroot -proot -P3314 test
Warning: Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 17
Server version: 5.6.15-log MySQL Community Server (GPL)

Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> CREATE TABLE IF NOT EXISTS `test` (
    ->   `i_instanceid` int(10) unsigned NOT NULL,
    ->   `i_descriptions` text NOT NULL,
    ->   PRIMARY KEY (`i_instanceid`)
    -> ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (0.91 sec)

mysql> INSERT INTO `test` (`i_instanceid`, `i_descriptions`) VALUES
    -> (1, '[{"type":"html","value":"\\u0425\\u043e\\u043b\\u043e\\u0434\\u0440\
\u044b\\u0436\\u0435\\u0441\\u0442\\u0432\\u043e 2013","color":"99ccff"},{"type"
:"html","value":"<div style=\\"white-space: nowrap; margin: 10px\\"><div style=\
\"white-space: nowrap; padding: 3px;\\"><div style=\\"width: 60px; height: 32px;
 vertical-align: top; display: inline-block;\\"><div style=\\"width: 48px; heigh
t: 32px; vertical-align: top; display: inline-block; border: 2px solid rgb(255,
255, 255);>\\"><div style=\\"position: absolute; width: 48px; height: 32px; vert
ical-align: top; display: inline-block; background-size: contain; background-ima
ge: url(http:\\/\\/cdn.dota2.com\\/apps\\/570\\/icons\\/econ\\/sockets\\/gem_sta
t.ea886ecaac62d6eb..."><\\/div><div style=\\"position: absolute; filter:alpha(op
acity=90); -moz-opacity:0.9; -khtml-opacity: 0.9; opacity: 0.9; width: 48px; hei
ght: 32px; vertical-align: top; display: inline-block; background-size: contain;
 background-image: url(http:\\/\\/cdn.dota2.com\\/apps\\/570\\/)\\"><\\/div><\\/
div><\\/div><div style=\\"vertical-align: top; display: inline-block; margin-lef
t: 12px padding: 2px\\"><span style=\\"font-size: 18px; color: rgb(255, 255, 255
)\\">\\u0423\\u043d\\u0438\\u0447\\u0442\\u043e\\u0436\\u0435\\u043d\\u043e \\u0
43a\\u0430\\u0437\\u0430\\u0440\\u043c: 0<\\/span><br><span style=\\"font-size:
12px\\">\\u0420\\u0443\\u043d\\u0430<\\/span><\\/div><\\/div><\\/div>"}]'),
    -> (2, '[{"type":"html","value":"\\u0425\\u043e\\u043b\\u043e\\u0434\\u0440\
\u044b\\u0436\\u0435\\u0441\\u0442\\u0432\\u043e 2013","color":"99ccff"},{"type"
:"html","value":"<div style=\\"white-space: nowrap; margin: 10px\\"><div style=\
\"white-space: nowrap; padding: 3px;\\"><div style=\\"width: 60px; height: 32px;
 vertical-align: top; display: inline-block;\\"><div style=\\"width: 48px; heigh
t: 32px; vertical-align: top; display: inline-block; border: 2px solid rgb(255,
255, 255);>\\"><div style=\\"position: absolute; width: 48px; height: 32px; vert
ical-align: top; display: inline-block; background-size: contain; background-ima
ge: url(http:\\/\\/cdn.dota2.com\\/apps\\/570\\/icons\\/econ\\/sockets\\/gem_sta
t.ea886ecaac62d6eb..."><\\/div><div style=\\"position: absolute; filter:alpha(op
acity=90); -moz-opacity:0.9; -khtml-opacity: 0.9; opacity: 0.9; width: 48px; hei
ght: 32px; vertical-align: top; display: inline-block; background-size: contain;
 background-image: url(http:\\/\\/cdn.dota2.com\\/apps\\/570\\/)\\"><\\/div><\\/
div><\\/div><div style=\\"vertical-align: top; display: inline-block; margin-lef
t: 12px padding: 2px\\"><span style=\\"font-size: 18px; color: rgb(255, 255, 255
)\\">\\u0423\\u0431\\u0438\\u0439\\u0441\\u0442\\u0432: 0<\\/span><br><span styl
e=\\"font-size: 12px\\">\\u0420\\u0443\\u043d\\u0430<\\/span><\\/div><\\/div><\\
/div>"}]');
Query OK, 2 rows affected (0.31 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> SELECT COUNT(*) FROM `test` GROUP BY `i_descriptions`;
+----------+
| COUNT(*) |
+----------+
|        1 |
|        1 |
+----------+
2 rows in set (0.42 sec)

mysql> SELECT GROUP_CONCAT(`i_instanceid`), COUNT(*) FROM `test` GROUP BY `i_des
criptions`;
+------------------------------+----------+
| GROUP_CONCAT(`i_instanceid`) | COUNT(*) |
+------------------------------+----------+
| 1,2                          |        2 |
+------------------------------+----------+
1 row in set (0.03 sec)

It's not clear why now we have one group instead of two (as the first query correctly shows).

Hello Dmitry,

Thank you for the bug report and test case.
Verified as described.

Thanks,
Umesh

#testcase:

drop table if exists t1;
create table if not exists `t1`(`a` int,`b` text)engine=innodb default charset=utf8;
insert into t1(a,b) values (1,repeat('a',1025)),(2,repeat('a',1024));
select count(*) from `t1` group by `b`;
select group_concat(`a`), count(*) from `t1` group by `b`;