Target reusing gift cards?

[MrTwoArms]

So a weird thing happened at Target today. I made 2 separate transactions, because the first was going to get me 2 $5 gift cards and I wanted to use those on the 2nd transaction. I get the 2 gift cards and use them towards Mad Men. The total was $10.82 and I had a dollar out ready to pay the tax, but the cashier says she doesn't need it and hands me the receipt and one of the gift cards back. I thought maybe the gift cards reduced the price to zero and I didn't pay have to pay the tax, but I've never had that happen before.

When I get home I notice the 1st gc had a $10 balance and the 2nd was for $5. The 1st receipt shows I only received 2 $5 gc, but 1 of them does say it has a new balance of $10. So that means that the gift card already had $5 on it before she swiped it to add the $5 I earned with that transaction.

Now I'm sitting at home with the gift card she handed back to me and it shows a $4.18 balance on the 2nd receipt (after paying for Mad Men). I decide to check the balance on the Target website and it is correct, but this is where it gets really weird. There are several different transactions with this same gift card. It was first issued 12/28 for $5, then redeemed on 1/3 in full. It was issued again that same day for $10 and then redeemed the following day in full at a different store (the store I ended up getting it). The next time this same card was issued was during my transaction today.

This is all very odd and I'm hoping someone here who works at Target can explain. Because the way it looks to me is that they are issuing the same gift cards over and over once they are emptied and the customer leaves them behind. If this is true, what is to keep someone who previously had one of these gift cards from using someone's balance? All they would need to do is write down the card # and access # and they would be able to use it online.

If anyone else has a gift card they got at Target recently, check it and let me know if you see anything similar.