Is this expected? (Index scanning)

Indexes on both void and lower(cust_name) here..

I get ->

EXPLAIN select * from invoice_master WHERE lower(cust_name) like 'mitch' AND
void = 'f' order by created LIMIT 100;
NOTICE:  QUERY PLAN:

Limit  (cost=2241.98..2241.98 rows=100 width=319)
  ->  Sort  (cost=2241.98..2241.98 rows=604 width=319)
        ->  Index Scan using invoice_cust_name on invoice_master
(cost=0.00..2214.09 rows=604 width=319)

The above query matches zero rows.

EXPLAIN SELECT * FROM invoice_master WHERE lower(cust_name) like '%mitch'
AND void = 'f' ORDER BY created LIMIT 100;
NOTICE:  QUERY PLAN:

Limit  (cost=4310.65..4310.65 rows=1 width=319)
  ->  Sort  (cost=4310.65..4310.65 rows=1 width=319)
        ->  Seq Scan on invoice_master  (cost=0.00..4310.64 rows=1
width=319)

The above query matches zero rows.

EXPLAIN SELECT * FROM invoice_master WHERE lower(cust_name) like 'mitch%'
AND void = 'f' ORDER BY created LIMIT 100;
NOTICE:  QUERY PLAN:

Limit  (cost=2241.98..2241.98 rows=100 width=319)
  ->  Sort  (cost=2241.98..2241.98 rows=604 width=319)
        ->  Index Scan using invoice_cust_name on invoice_master
(cost=0.00..2214.09 rows=604 width=319)

The above query matches 53 rows..

PostgreSQL 7.1.1, FreeBSD 4.2, 73408 records in the invoice_master table and
it's all freshly vacuum analyze 'd...

 I'm just wondering if I'm doing something extremely silly here.. Thanks!!

-Mitch