BUG with UNIQUE clause

Hi,

The UNIQUE constraint doesn't work on a field if I use a DEFAULT clause on a table.

The following table works with UNIQUE constraint:

create table cltclt001(
tcid int2,
tcnom text unique
);

but this one accept several same tcnom value:

create table cltclt001(
tcid int2 default nextval('cltcls001'),
tcnom text unique
);

What's wrong with my table ?

Thanks in advance.

Stephane FILLON