How did you use the debit card? Yes, it all depends on how you use it.
Was it as debit (you use your pin number)? If so, I'd suggest you call the bank and see what's going on.
Was it as credit (you didn't use your pin number)? If that was the case, then the bank can only hold the money for a certain amount of time. If the merchant does not collect within that time frame, the hold falls off and the money is put back into the account. I can take up to 10 business days until the merchant goes to collect. When he does, the merchant will take the money out regardless of funds in the account or not.
Sounds like the merchant has yet to actually collect it; they haven't batched out all the transactions that have been collecting.