This used to work in 10.0 and 10.1:

set time_zone='Europe/Moscow';

create table t1 (a timestamp);

set timestamp=1288481126;

insert t1 values (null);

select a, unix_timestamp(a) from t1;

but in 10.2 it returns 1288477526 (one hour earlier).

Because both 1288481126 and 1288477526 are written as 2010-10-31 02:25:26 in time zone Europe/Moscow, and intermediate timestamp→datetime→timestamp conversion loses information.