This happened to me several times. I often use my debit card for transactions, like buying lunch or stuff. Problem arises when I have low balance, I first check the ATM and check my balance before I use the card. having checked the balance, I used my card for another transaction. Now problem arises when previous debit card transactions do not reflect in several days, and when they reflect, my balance become negative and I get charged for insufficient fund. The thing I don't like is that the balance shown in the ATM does not reflect the "current" balance. There are still some pending transactions and for whatever reason, they don't get reflected quickly. My other debit card is like real time. Whenever I use it, it quickly reflects in the balance on the ATM.