I do not know if this should be a bug or a feature request.
anyway, I was making a block that generates tree items. this is similar to the furnace. And I was wanting to use hoppers to input into the input slot and (when the hopper is placed below the block) only take items out of the output slot. I then went and tested it and the hopper inputs and outputs to any of the slots starting with slot 0.
In minecraft itself, the hoppers can input into the furnace only to the input slots and take out from only the output slots.
It would be really nice if this was fixed and if it was not even in the program, to begin with adding it to mcreator.
Issue comments
This can't be controlled by MCreator directly right now, unfortunately. Right now you can manually override
public boolean canInsertItem(int index, ItemStack itemStackIn, EnumFacing direction)
in TileEntity of the block to make this work. I will open this ticket back and will try to fix this for future versions.
If you bind GUI to the block and use inherited inventory for slots, hoppers will work.