Bug with group by & group_concat

Hello,

We spot a bug with group by & group_concat, here is the simplified test case :

– Step 1 create a temp table with 2 different rows of 1025 char (datatype is text)

drop temporary table if exists _test;

create temporary table _test as

select lpad('a', 1025, '0') as chaine

union

select lpad('b', 1025, '0');

– This result is OK

select *

from _test

group by chaine;

– In this query, all is grouped, it should not !

select group_concat(chaine)

from _test

group by chaine;

– we found an ugly workaround...

select group_concat(chaine)

from _test

group by crc32(chaine);

This is an upstream bug, i reported it here :
http://bugs.mysql.com/bug.php?id=78383

Tested on MySQL 5.5.39, MySQL 5.6.26, MariaDB 10.0.19