No, nothing custom at all. It seems to be dependent on the number of items the user chooses to display within the category. llegrand was able to duplicate, and it's not browser specific.
i.e. Choose to display 25 items and the duplicates change. In fact, there are even items that don't belong in that category. Go to 40 items to display and the duplicates change again.
I am running 1.2.1
Caches have been cleared also. The fact that llegrand can see it tells me it's the cart, not me.
Here's the link,
https://naturalhandcraftedsoaps.com/secure/nearly-natural-hand-crafted-soapsNotice that Sweepea and red clover tea are repeated on the second page.
Switch the view to 45 items, the dupes are gone. Change it to 25 and you'll see a soap Vanilla Sugar Goats Milk at the bottom of the first page that is out of category, it doesn't show when the quantity to view is 40 or 45.