If you put a chest minecart into a chest boat below a hopper and put items on it the hopper will put items into the boat and the minecart at the same time and duplicate it.

Steps to reproduce

1. Place a rail by right clicking
2. Place a chest minecart on it by right clicking
3. Place a chest boat by right clicking
4. Push the chest boat into the minecart
5. Place a hopper above by right clicking
6. Put 10 netherite ingots into the hopper by opening the hopper by right clicking
7. Wait

Observed behavior

The hopper places the items into the minecart and boat at the same time and duplicate it. At the end you have 20 netherote ingots.

Expected behavior

The hopper does not duplicate items.