Not sure if this is really a bug, or just a suggestion for an improvement, but I think that the Customer Statement layout is confusing.

Both new invoices *and* customer receipts/payments are shown on the statement as positive numbers in the same column.  I think that for the statement to be a better representation you need either:

• to use two columns, one for invoices and one for receipts, to separate them better, or
• to show the receipts/payments as negative numbers, so that the running total is more logically presented.