Sorry for not answering, but I've been cut from the net.
I can't send you my database, because since then I dropped it
and recreated.
As my thought it has something to do with triggers. While running
a live database I've created/dropped a trigger function a few times
that operated on that specific table.
As far as I remember pk constraint was there.
I wish I could help you more...
--
Marcin Gil
marcin.gil @ audax.com.pl, tel. 694972082
OIS Audax Sp. z o.o., ul. Barlickiego 4, 97-200 Tomaszów Mazowiecki
tel/fax (44) 7247530, 7244401