BUG #13766: weird ts_headline/ts_vector/ts_query behaviour

The following bug has been logged on the website:

Bug reference: 13766
Logged by: Calendar 42
Email address: aslesha(dot)akella(at)gmail(dot)com
PostgreSQL version: 9.2.4
Operating system: gentoo
Description:

We are trying to make text search for a word "goede" and "goed". It got the
following results with different languages.

select ts_headline(replace(strip(to_tsvector('dutch', 'Goede
vrijdag'))::text,'''',''), plainto_tsquery('dutch', 'goede'));
ts_headline
--------------
goed vrijdag

select ts_headline(replace(strip(to_tsvector('dutch', 'Goede
vrijdag'))::text,'''',''), plainto_tsquery('dutch', 'goed'));
ts_headline
--------------
goed vrijdag

(NOTE: this works)
select ts_headline(replace(strip(to_tsvector('english', 'Goede
vrijdag'))::text,'''',''), to_tsquery('english', 'goed'));
ts_headline
---------------------
<b>goed</b> vrijdag

select ts_headline(replace(strip(to_tsvector('english', 'Goede
vrijdag'))::text,'''',''), to_tsquery('english', 'goede'));
ts_headline
--------------
goed vrijdag

this works too but didnt understand how, because the stem for the word
"Goede" in 'simple' is 'goede'. But 'simple' works for 'goed' and not for
'goede'

select ts_headline(replace(strip(to_tsvector('simple', 'Goede
vrijdag'))::text,'''',''), to_tsquery('simple', 'goed'));
ts_headline
----------------------
<b>goede</b> vrijdag

select ts_headline(replace(strip(to_tsvector('simple', 'Goede
vrijdag'))::text,'''',''), to_tsquery('simple', 'goede'));
ts_headline
---------------
goede vrijdag