Mistake in my query or Index Scan on subquery failure? (7.4)

Hello,
I have a problem with this simple query :

explain select * from ref_artikel a where a.artnr in ( 351275 , 351346 ,
293082 ) LIMIT 20 OFFSET 0 ;
QUERY PLAN

----------------------------------------------------------------------------
------------------------------------------------------
Limit (cost=0.00..9.06 rows=3 width=299)
-> Index Scan using ref_artikel_pkey, ref_artikel_pkey, \
ref_artikel_pkey on ref_artikel a (cost=0.00..9.06 rows=3 width=299)
Index Cond: ((artnr = 351275) OR (artnr = 351346) OR (artnr =
293082))
(3 rows)

Is it okay , that the word ref_artikel_pkey will be repeated for each
condition ?

How can i optimize this, i have a number of up to 3000 "artnr" cond. to
check for equality
( and more tables joined over this query which i left away for better
understanding ) ,
is a "(x=1) or (x=2)..." faster than "x in 1,2... " at this large number of
checks ?

Maybe this is the hash-joined bug marked for this 7.4 postgresql....
I consider upgrading to 7.41 on another testing server....

Thx for ideas,
Andre