Date with timezone format

I've notice the following behaviour, and would like some comments about the
way to interpret it.

I have the following table :
                          Table "pointage"
    Attribute    |           Type           |        Modifier
-----------------+--------------------------+------------------------
 cd_collab       | numeric(3,0)             | not null
 dt_debut        | timestamp with time zone | not null
 dt_fin          | timestamp with time zone |
 cd_typ_pointage | numeric(2,0)             | not null
 comm            | text                     |
 dt_creat        | timestamp with time zone | not null
 dt_modif        | timestamp with time zone | not null default now()
Index: pk_pointage

and the following configuration :

NOTICE:  DateStyle is SQL with European conventions
NOTICE:  Time zone is unknown

When I use (in psql) :
insert into POINTAGE (CD_COLLAB,DT_DEBUT,CD_TYP_POINTAGE,DT_CREAT,DT_MODIF)
values ( 1,'28/10/2001 09:26 GMT+01:00',1,'28/10/2001
09:26:16GMT+01:00','28/10/2001 09:26:16 GMT+01:00');
or
insert into POINTAGE (CD_COLLAB,DT_DEBUT,CD_TYP_POINTAGE,DT_CREAT,DT_MODIF)
values ( 1,'28/10/2001 09:26 GMT+01:00',1,'28/10/2001
09:26:16GMT+01:00','28/10/2001 09:26:16 GMT+01:00');

a select then returns :
 cd_collab |          dt_debut          | dt_fin | cd_typ_pointage | comm |
dt_creat          |          dt_modif
-----------+----------------------------+--------+-----------------+------+-
---------------------------+----------------------------
         1 | 28/10/2001 10:26:00.00 GMT |        |               1 |      |
28/10/2001 10:26:16.00 GMT | 28/10/2001 10:26:16.00 GMT

but when I use :
insert into POINTAGE (CD_COLLAB,DT_DEBUT,CD_TYP_POINTAGE,DT_CREAT,DT_MODIF)
values ( 1,'28/10/2001 09:26+01:00',1,'28/10/2001
09:26:16+01:00','28/10/2001 09:26:16+01:00');

a select returns the following results which is right :
 cd_collab |          dt_debut          | dt_fin | cd_typ_pointage | comm |
dt_creat          |          dt_modif
-----------+----------------------------+--------+-----------------+------+-
---------------------------+----------------------------
         1 | 28/10/2001 08:26:00.00 GMT |        |               1 |      |
28/1
0/2001 08:26:16.00 GMT | 28/10/2001 08:26:16.00 GMT

So it seems that the former syntax is not right and is interpreted as 9:26
with GMT TimeZone, One hour is then added to the date. Is this right ??

If it is, why, with SQL datestyle, is it a bad syntax ?

Emmanuel Guyot