Array casting in where : unexpected behavior

Good Morning list,
we have a strange situation here, manifested in the following queries :
Postgresql version : 9.3.10

dynacom=# select * FROM (select vals from fb_forms_defs fd, fb_reports_dets rd where fd.id=rd.fdid and fd.dbtag='observer') as qry;
vals
---------
{7078}
{13916}
{7078}
{2054}
{7078}
{13916}
{2054}
{13916}
{2054}
{8844}
{13916}
{13916}
{2054}
{13916}
{13916}
{13916}
{2054}
{2054}
{13916}
{13916}
{13916}
{13916}
{13916}
{13916}
{13916}
(25 rows)

dynacom=#

dynacom=# select * FROM (select vals from fb_forms_defs fd, fb_reports_dets rd where fd.id=rd.fdid and fd.dbtag='observer') as qry WHERE vals[1]::int=8844;
ERROR: invalid input syntax for integer: "19/10/2015"
dynacom=#

dynacom=# select vals[1]::int FROM (select vals from fb_forms_defs fd, fb_reports_dets rd where fd.id=rd.fdid and fd.dbtag='observer') as qry;
vals
-------
7078
13916
7078
2054
7078
13916
2054
13916
2054
8844
13916
13916
2054
13916
13916
13916
2054
2054
13916
13916
13916
13916
13916
13916
13916
(25 rows)

dynacom=#

dynacom=# select vals1 FROM (select vals[1]::int as vals1 from fb_forms_defs fd, fb_reports_dets rd where fd.id=rd.fdid and fd.dbtag='observer') as qry;
vals1
-------
7078
13916
7078
2054
7078
13916
2054
13916
2054
8844
13916
13916
2054
13916
13916
13916
2054
2054
13916
13916
13916
13916
13916
13916
13916
(25 rows)

dynacom=# select vals1 FROM (select vals[1]::int as vals1 from fb_forms_defs fd, fb_reports_dets rd where fd.id=rd.fdid and fd.dbtag='observer') as qry WHERE vals1=8844;
ERROR: invalid input syntax for integer: "19/10/2015"
dynacom=#

^^^ is this normal? Isn't vals1 guaranteed to be integer since its the type defined in the subselect ?

However this seems to work :

dynacom=# select * FROM (select vals from fb_forms_defs fd, fb_reports_dets rd where fd.id=rd.fdid and fd.dbtag='observer') as qry WHERE vals[1] ~ E'^\\d+$' AND vals[1]::int=8844;
vals
--------
{8844}
(1 row)

dynacom=#

--
Achilleas Mantzios
IT DEV Lead
IT DEPT
Dynacom Tankers Mgmt