Postgres regexp matching failure?

I have an regular expression, wich works fine in Java or python, but I
don't seem to be able to make it work in postgres. Regular expression
needs to match everything begining with '+' (plus sign) or letters
'STOP', 'stop', 'StoP', or any other combination pronounced 'stop'.

Here is the python example:

>>> import re
>>> p = re.compile(r'^\s*(?:[\+|-]|(?:[sS][tT][oO][pP]\b)).*$')
>>> p.match('+mario').group(0)
'+mario'
>>> p.match('+mario works').group(0)
'+mario works'
>>> p.match('mario works').group(0)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
AttributeError: 'NoneType' object has no attribute 'group'
>>> p.match('stop works').group(0)
'stop works'
>>>

Now, here is what happens if I try this in postgres:

pulitzer2=# select '+mario' ~ '^\s*(?:[\+|-]|(?:[sS][tT][oO][pP]\b)).*
$';
?column?
----------
t
(1 row)

This one is ok.

pulitzer2=# select '+mario works' ~ '^\s*(?:[\
+|-]|(?:[sS][tT][oO][pP]\b)).*$';
?column?
----------
t
(1 row)

This one is also ok.

pulitzer2=# select 'mario works' ~ '^\s*(?:[\
+|-]|(?:[sS][tT][oO][pP]\b)).*$';
?column?
----------
f
(1 row)

Same as this one, also ok.

pulitzer2=# select 'stop works' ~ '^\s*(?:[\
+|-]|(?:[sS][tT][oO][pP]\b)).*$';
?column?
----------
f
(1 row)

Here, postgres should return true, but it gives me false.

I'd appreciate any hints on what is wrong here.

Thank you in advance,

Mario
--
Mario Splivalo
Mob-Art
mario(dot)splivalo(at)mobart(dot)hr

"I can do it quick, I can do it cheap, I can do it well. Pick any two."