Optimizer failure on update w/integer column

Is there a documented problem with optimizing integer key fields
in 7.3.3?

I have two tables.  One was extracted from the other and has
the following four columns.

    mtranmemid   varchar(8),
    mtranseq     integer,
    mtransts     char,
    mtranmemtp   varchar(2)

mtranseq is a unique index on both tables and contains no nulls.

When I try to do an update, it takes several hours.  Here's what
explain says about the query:

explain update missing_ids
set mtransts = a.mtransts,
mtranmemtp = a.mtranmemtp
from memtran as a
where a.mtranmemid = missing_ids.mtranmemid
and a.mtranseq = missing_ids.mtranseq

                                   QUERY PLAN
--------------------------------------------------------------------------------
 Hash Join  (cost=9231.64..58634.93 rows=1 width=48)
   Hash Cond: ("outer".mtranseq = "inner".mtranseq)
   Join Filter: ("outer".mtranmemid = "inner".mtranmemid)
   ->  Seq Scan on memtran a  (cost=0.00..22282.57 rows=714157 width=26)
   ->  Hash  (cost=6289.91..6289.91 rows=351891 width=22)
         ->  Seq Scan on missing_ids  (cost=0.00..6289.91 rows=351891 width=22)
--
Mike Nolan