This isn't something that's unique to Ebates -- on any rewards program, if you use a coupon from another website (or from a snail-mailed catalog), it can invalidate your shopping reward. What happens is that some coupon codes are unique to a particular coupon site and when you use it, it shifts the commission on that sale from the rewards program to the coupon site. If the rewards program doesn't get commission for your sale, they can't give you your cut (your points or cash back).
The codes that come from mailed catalogs work the same way. To the retailer, like Avon for example, the code says, "My catalog is what generated this sale, because the buyer used a free shipping code from my catalog... why do I need to give Ebates or MyPoints, etc., a commission on the sale?"
So the moral of the story is, either get your coupon codes directly from the rewards program where you're shopping, or figure out what's the better deal: the cash back or the coupon, and if it's the coupon, go ahead and try to combine it with cash back... but if it's the cash back, don't jeopardize it by trying to add on an additional, smaller discount using a code.
The thing with store pickup is also something that's universal (at least, for certain merchants like
Walmart, CircuitCity, and Sears). I think it's because when you go to pick up your item, that's when you pay. And because the transaction occurs in-store, there's no way for the rewards program to track your sale.
Anyway, I just wanted to explain that it's not just an Ebates thing, or due to any one rewards program's rules; it has to do with the way merchants have their commission systems set up and you'd have had the same results on any rewards program where you used an outside coupon code or did an in-store pickup.
Hope this helps!
