I also had this multiplication. I made one, dragged it to a stone deposit, collected some stone, started dragging it home, game froze, character turned invisible, assets in world turned invisible, I closed game, reentered and had two carts holding the same amount of items.
All items usable, still have both carts.
I added 6 stones in my handcart and once I used them my cart still had another 6 stones.
If I click the icon to see the contents of the cart with my character positioned next to it, then the cart is empty. If I move my character away and then check the cart contents the stones are shown.