INFORMIX SERVER / 5725A3900 / C10 - IDS 12.10

The following query with DISTINCT and LEFT JOIN returns wrong 
results : 
 
select distinct t1.c_2, t2.c_2, t1.id_1, t2.c_2 is not null or 
(t1.c_2 <> '') 
from gt_test t1 
left join gt_test t2 on t1.id_1 = t2.id_1 and t1.c_2 <> t2.c_2 
where t2.c_2 is not null or (t1.c_2 <> ''); 
 
It returns rows, however in version 11.70 the same query returns 
no rows.

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* USERS AFFECTED:                                              * 
* SQL QUERY with ANSI LEFT OUTER JOIN                          * 
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* PROBLEM DESCRIPTION:                                         * 
* See Error Description                                        * 
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* RECOMMENDATION:                                              * 
* Update to IBM Informix Server 12.10.xC6                      * 
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Problem Fixed In IBM Informix Server 12.10.xC6

see CQ remarks

Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :

12.06.2015
30.12.2015
30.12.2015

12.10.xC6