Hey,
I'm trying to have it work so that on pressing a custom button in a gui that extends a GuiContainer the contents of the container gets modified. For example, I have it so that upon the button press, it calls a function in the TileEntity linked to the gui which copies the item stack in slot 0 and puts it in slot 1, and empties slot 0. It also adds additional NBT data to the stack. Unfortunately, when you try to take the new ItemStack out of slot 1, it resets to before you press the button, with the old stack in slot 0 with no additional data.
Does anyone know how to make it so that the client side and server side containers synchronise and have the same contents?