FBA Question - Is this Ethical? Should I be Concerned?

A few weeks ago I discovered a product on clearance at a local store. Turns out the item was selling for a pretty significant profit on Amazon so I sent it in. After my supply ran out I looked around to find another source but I also realized that this product had a duplicate listing on Amazon. The main listing, with the lower (more favorable) ranking, better pictures, and more information sold for the price you would pay for it at the store. The second listing sold for a few times that price and still had a decent sales rank.

So I ended up buying a bunch of these items and sending them in and they all sell out pretty quickly. I just placed a re-order when I got a return request (I don't know the reason why yet) and it had me worried so I checked out the two identical listings. Turns out the Lower Sales (which sells for less) ranked item is the item I am selling. The listing that I am selling under is actually for a smaller quantity.

The smaller package size is no longer sold (per the manufacturer) which is probably why it went on clearance. I'm concerned that this could result in returns or negative action from Amazon but than I'm not exactly sure why. At the end of the day the listing is identical except for a small weight description at the bottom of the details. And if anything the customer is getting more of the product than they thought. The packaging is exactly the same only a larger size (about twice as big).

What are your thoughts? I really don't want to end up with a few hundred of these items after a ton of returns!