When a non-trusting ocelot is leashed, feeding it will consume items client-side, but not server-side.

To reproduce

1. Summon an ocelot
2. Leash it to a fence
3. Give yourself a stack of cod
4. Switch into Survival
5. Feed the cod to the ocelot
   → The cod items will be consumed, with only the first one actually doing anything
6. Pick up the cod item stack in your inventory
   → The item count resets to 63

Video

Minecraft 1.16.5 - Singleplayer 2021-06-03 16-46-25.mp4