On this state of affairs, neither tackle A nor tackle B had a adequate steadiness to pay 0.5 BTC by itself. The 2 collectively did have sufficient. So, the purchasers are clever sufficient mix the quantities of two addresses collectively with a purpose to meet the specified transaction quantity.
Sadly, the mix has the impact of sending bitcoins to your self as “change” within the transaction. On this state of affairs, all the obtainable steadiness was break up between tackle A and tackle B. In combining these with a purpose to fulfill the fee to C, some was consolidated as “change” into tackle B.
Consider it mathematically, as effectively. This exhibits the equilibrium, from the standpoint of the accounts you management.
steadiness(A) + steadiness(B) = payment_to(B) + payment_to(C) + transaction_fee(0.0005)
That is the transaction.
steadiness(A) + steadiness(B) - payment_to(C) - transaction_fee(0.0005) = payment_to(B)
That payment_to(B) is the change.
Sadly, due to the variety of confirmations the purchasers wait earlier than permitting one to spend incoming transactions, the steadiness is current however unavailable to spend for a number of minutes, or as a lot as hour or extra.
Purchasers ought to deal with this higher by warning if transaction about to be despatched will create this complicated scenario.