query plan wierdness?

Can someone explain what I'm missing here? This query does what I
expect--it uses the "foo" index on the openeddatetime, callstatus,
calltype, callkey fields:

elon2=# explain analyse select * from call where aspid='123C' and
OpenedDateTime between '2000-01-01 00:00:00.0' and '2004-06-24
23:59:59.999' order by openeddatetime desc, callstatus desc, calltype
desc, callkey desc limit 26;

QUERY PLAN

------------------------------------------------------------------------
------------------------------------------------------------------------
-----------------------------
Limit (cost=0.00..103.76 rows=26 width=297) (actual time=0.07..0.58
rows=26 loops=1)
-> Index Scan Backward using foo on call (cost=0.00..1882805.77
rows=471781 width=297) (actual time=0.06..0.54 rows=27 loops=1)
Index Cond: ((openeddatetime >= '2000-01-01
00:00:00-07'::timestamp with time zone) AND (openeddatetime <=
'2004-06-24 23:59:59.999-07'::timestamp with time zone))
Filter: (aspid = '123C'::bpchar)
Total runtime: 0.66 msec
(5 rows)

However, this query performs a sequence scan on the table, ignoring the
call_idx13 index (the only difference is the addition of the aspid field
in the order by clause):

elon2=# explain analyse select * from call where aspid='123C' and
OpenedDateTime between '2000-01-01 00:00:00.0' and '2004-06-24
23:59:59.999' order by aspid, openeddatetime desc, callstatus desc,
calltype desc, callkey desc limit 26;

QUERY PLAN

------------------------------------------------------------------------
------------------------------------------------------------------------
------------------------------------------------------------
Limit (cost=349379.41..349379.48 rows=26 width=297) (actual
time=32943.52..32943.61 rows=26 loops=1)
-> Sort (cost=349379.41..350558.87 rows=471781 width=297) (actual
time=32943.52..32943.56 rows=27 loops=1)
Sort Key: aspid, openeddatetime, callstatus, calltype, callkey
-> Seq Scan on call (cost=0.00..31019.36 rows=471781
width=297) (actual time=1.81..7318.13 rows=461973 loops=1)
Filter: ((aspid = '123C'::bpchar) AND (openeddatetime >=
'2000-01-01 00:00:00-07'::timestamp with time zone) AND (openeddatetime
<= '2004-06-24 23:59:59.999-07'::timestamp with time zone))
Total runtime: 39353.86 msec
(6 rows)

Here's the structure of the table in question:

Table "public.call"
Column | Type | Modifiers
------------------+--------------------------+-----------
aspid | character(4) |
lastmodifiedtime | timestamp with time zone |
moduser | character(13) |
callkey | character(13) |
calltype | text |
callqueueid | text |
openeddatetime | timestamp with time zone |
assigneddatetime | timestamp with time zone |
closeddatetime | timestamp with time zone |
reopeneddatetime | timestamp with time zone |
openedby | text |
callstatus | character(1) |
callpriority | text |
callreasontext | text |
keyword1 | text |
keyword2 | text |
callername | text |
custfirstname | text |
custlastname | text |
custssntin | character(9) |
custssnseq | text |
custdbccode | character(9) |
custlongname | text |
custtypecode | character(2) |
custphone | text |
custid | character(9) |
assigneduserid | character varying(30) |
historyitemcount | integer |
callertype | text |
callerphoneext | text |
followupdate | text |
hpjobnumber | character(11) |
Indexes: call_idx1 unique btree (aspid, callkey),
call_aspid btree (aspid),
call_aspid_opendedatetime btree (aspid, openeddatetime),
call_idx10 btree (aspid, keyword1, openeddatetime, callstatus,
calltype
, custtypecode, custid, callkey),
call_idx11 btree (aspid, keyword2, openeddatetime, callstatus,
calltype
, custtypecode, custid, callkey),
call_idx12 btree (aspid, custtypecode, custid, openeddatetime,
callstat
us, calltype, callkey),
call_idx13 btree (aspid, openeddatetime, callstatus, calltype,
callkey),
call_idx14 btree (aspid, callqueueid, callstatus, callkey),
call_idx2 btree (aspid, callqueueid, openeddatetime,
custtypecode, call
status, callkey),
call_idx3 btree (aspid, assigneduserid, openeddatetime,
custtypecode, c
allstatus, callkey),
call_idx4 btree (aspid, custid, custtypecode, callkey,
callstatus),
call_idx7 btree (aspid, calltype, custtypecode, custid,
callstatus, cal
lkey),
call_idx9 btree (aspid, assigneduserid, callstatus,
followupdate),
foo btree (openeddatetime, callstatus, calltype, callkey)

TIA,

-Joel

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