issues with libpq interface

We have two situations that have arisen while using libpq thru CMUCL
bindings in our UncommonSQL package.  We have a multi-processing
application which uses a pool of database connections to perform DB
queries.

The first one is that we are getting unexpected retun values from
pgresultstatus after calling pgexec, a value of PGRES_TUPLES_OK.  The
thing is that we're not sending a SELECT, just UPDATES, INSERTS and
DELETES.  My understanding is that none of those return tuples.

Here is the message our interface spits out.

;; Warning, database-execute-command: Recieved tuples ok in response  to UPDATE WCO_ALLOCATION SET CANCELLED_TIME =
'2001-01-12 16:50:10+00',DELETED_AGENT_ID = 0,PICKUP = 'f',RETURN_AGENT_ID =  7104,NON_EXPIRING = 'f',INSTRUCTIONS =
'',BUILDING_PASSES=  'NIL',ACCOMPANYING_PEOPLE = 'NIL',PICKUP_PEOPLE = 'NIL',COMMENTS =  '',CREATED_TIME = '2001-01-12
16:50:50+00',REPEAT_RULE=  'NIL',END_TIME = '2001-01-16 17:48:00+00',START_TIME = '2001-01-12  16:50:50+00',AGENT_ID =
6761,CUSTOMER_ID= 3970,LOCATION_ID =  4,ALLOCATION_TYPE = 'COMPLETED-CHECKOUT',ALLOCATION_ID = 34166  WHERE
WCO_ALLOCATION.ALLOCATION_ID= 34166
 

So, is it possible for an UPDATE to correctly return PGRES_TUPLES_OK,
or are we seeing some confusion in the backend or libpq due to load
and multi-processing?

Also, unrelated, I think, to the above issue, we are getting the
following message intermittently:

Backend message type 0x50 arrived while idle

I cannot find any more information about this message in the
documentation, so I don't know what type of message that is.