access linked tables

Hi,
Not sure if this is the right place to ask this - I'm just getting started
converting an access database to use postgresql as the database and access
as the front end.  I'm looking at whether its ok to just use linked tables
and bound forms, or whether I need to use a combination of ADO, pass-through
queries, unbound forms, and explicit code to comunicate with the db.

My question is, although my postgres tables have PKs, with linked tables
when access generates a query to do an update it doesn't use the pk in the
where clause, but does something like:
update tablename set field1 = 'newvalue1', field2 = 'newvalue2'....
where field1 = 'oldvalue1' and field2 = 'oldvalue2'... etc etc for all the
fields in the table.

This seems unneccesary and inefficient to me - is it normal behaviour for
access linked tables?  Is there something I can do to tell access to just
use the pk?

I'm using postgres 7.0.2, ODBC driver 6.5

Thanks,
Tamsin