Comment 8 for bug 773282

Credit Card accounts are not the same as regular bank accounts.

Bank account statements show how much money you have deposited, so credits are + and outbound payments (purchases) are -

With a Credit Card, when you make a purchase the CC company pays for the item, and adds the price to your account.
When you then make a payment you are covering the debt.
Credit card statements show how much you *owe* so purchases are + and "payments" (Credits to the CC account) are -