Tested on forge 1.20

Currently, calling insertItem(slot, stack, simulate) on an inventory from sophisticated mods causes items to be modified outside of the slot index specified.

Reproduction steps:

• Occupy slot 0 of a sophisticated inventory with some item
• Call insertItem(0, stack, false) with 'stack' being some other item that will not stack
• insertItem returns ItemStack.EMPTY and slot 1 was filled

I assume due to how many layers these handlers have to be set up with, its not trivial to maintain the slot convention,
but currently this leads to duplication glitches with Create 6. I'm happy to help with more details/troubleshooting

Thanks!