When processing credit/debit cards there is a choice made by the company on how they want to go about doing it. The options are Authorization/Capture and Sale.
For online transactions that require the delivery of goods, companies are supposed to start by initially
Authorizing the transaction. This signals your bank to mark the funds but it does not actually transfer them. Once the company is actually shipping the goods, they will send a
Capture command that tells the bank to go ahead and transfer the funds. There can be a time delay between the two actions. 3 days is fairly common, but longer can certainly be seen. It normally takes a week for a gas station local to me to clear their transactions.
The second one, a
Sale is normally used for online transactions in which a service is immediately delivered or a Point of Sale transaction (buying something in person at a store). This action wraps up both an Authorization and Capture into a single step.
Now, not all systems have the same requirements. It is actually fairly common for people who play online games to "accidentally" authorize funds to be transferred from their bank. Processing those refunds can be fairly expensive. However, if the company simply performs an Authorization and never issues a capture then it's as if the transaction never occurred and the costs involved to the company are much smaller (close to zero)
I'd suspect they have a high degree of parents claiming their kids were never authorized to perform transactions or that fraud was involved. If this is the case then it would be in the company's interest to authorize the transaction, apply the credits to your account then wait a few days before actually capturing the funds from the bank.
Depending upon the amount of time for the wait your bank might have silently rolled back the authorization. When it came time for the company to capture, then they'd just reissue it as a sale.
I hope that makes sense. The point is, this is actually fairly common. Not just for games but for a whole host of areas in which fraud might exist (like getting gas).