FULLTEXT searching woes - why does this happen

[Ter Chrng Ng]

When I query

SELECT * FROM csim_debitor WHERE MATCH (cust_index) AGAINST ('+SUP* ' IN BOOLEAN MODE) ORDER BY cust_no ASC LIMIT 19,20

I got matched with

SUPPLY and SUPPLIES ( this is correct)

However
When I query

SELECT * FROM csim_debitor WHERE MATCH (cust_index) AGAINST ('+SUPP* ' IN BOOLEAN MODE) ORDER BY cust_no ASC LIMIT 19,20;

I got an empty set

Note: I did rebuild the table several times.