Hm, this seems odd---I thought a credit was a balance increase on an expense or asset account, or a balance decrease on an income or liability account, so that (for example) buying lunch with a credit card is a debit to the credit card (liability) and a credit to, say, my dining account (expense). I'd think of bitcoins as an asset, so that an increase in balance should be a credit. It's a debit from somewhere, sure---in my case, usually "mining", an income account.
Is Gnucash using the terminology backward?
A credit card balance, alone, is a "credit" balance.
When buying lunch with your credit card:
Debit the Meals & Entertainment expense account
Credit the credit card liability account
When you make a payment to the credit card account:
Debit the credit card liability account for the amount of the payment
Credit the checking account for the amount of the payment
Increases to income are always credits. The corresponding entry is a debit, usually to either cash or accounts receivable.