Curious... why so many transaction_lines?

I just happened to run a query for a specific transaction:

 SELECT tl.transaction_line_id, tl.amount, tl.transaction_order FROM TRANSACTIONS AS t  INNER JOIN TRANSACTION_LINES AS tl ON tl.Transaction_id = t.transaction_id  WHERE t.Transaction_ID = 8528 

Here are the results (I hope they are formatted decent)
transaction_line_id    amount    transaction_order  0    225    0  1    -225    1  2        2  3        3  4        4  5        5  6        6  7        7  8        8  9        9  10        10  11        11  12        12  13        13  14        14  15        15  16        16  17        17  18        18  19    0    19

My main question is why does a transaction with a SINGLE line item have 20 line item records?  I can speculate what some of them are:
0) the item sold
1) a credit that might have been applied
19) shipping (that was zeroed out)

What about 2-18?  What are they, why are they there?