diff --git a/inventory.lua b/inventory.lua
index 88cb6be..86b1536 100644
--- a/inventory.lua
+++ b/inventory.lua
@@ -4,12 +4,16 @@ local pipeworks_enabled = minetest.get_modpath("pipeworks") ~= nil
 -- pos: the position of the Digilines chest node.
 -- action: the action string indicating what happened.
 -- stack: the ItemStack that the action acted on (optional).
+-- from_slot: the slot number that is taken from (optional).
+-- to_slot: the slot number that is put into (optional).
 -- side: which side of the chest the action occurred (optional).
-local function send_message(pos, action, stack, side)
+local function send_message(pos, action, stack, from_slot, to_slot, side)
 	local channel = minetest.get_meta(pos):get_string("channel")
 	local msg = {
 		action = action,
 		stack = stack and stack:to_table(),
+		from_slot = from_slot,
+		to_slot = to_slot,
 		-- Duplicate the vector in case the caller expects it not to change.
 		side = side and vector.new(side)
 	}
@@ -113,27 +117,88 @@ minetest.register_node("digilines:chest", {
 				-- Here, direction = direction item is moving, which is into
 				-- side.
 				local side = vector.multiply(direction, -1)
-				send_message(pos, "toverflow", stack, side)
+				send_message(pos, "toverflow", stack, nil, nil, side)
 			end
 			return ret
 		end,
-		insert_object = function(pos, _, stack, direction)
+		insert_object = function(pos, _, original_stack, direction)
 			-- Here, direction = direction item is moving, which is into side.
 			local side = vector.multiply(direction, -1)
-			local leftover = minetest.get_meta(pos):get_inventory():add_item("main", stack)
-			local leftover_count = leftover:get_count()
+			local inv = minetest.get_meta(pos):get_inventory()
+			local inv_contents = inv:get_list("main")
+			local any_put = false
+			local stack = original_stack
+			local stack_name = stack:get_name()
 			local stack_count = stack:get_count()
-			if leftover_count ~= stack_count then
-				-- Some items were added. Report them.
-				stack:set_count(stack_count - leftover_count)
-				send_message(pos, "tput", stack, side)
-				check_full(pos, stack)
+			-- Walk the inventory, adding items to existing stacks of the same
+			-- type.
+			for i = 1, #inv_contents do
+				local existing_stack = inv_contents[i]
+				if not existing_stack:is_empty() and existing_stack:get_name() == stack_name then
+					local leftover = existing_stack:add_item(stack)
+					local leftover_count = leftover:get_count()
+					if leftover_count ~= stack_count then
+						-- We put some items into the slot. Update the slot in
+						-- the inventory, tell Digilines listeners about it,
+						-- and keep looking for the a place to put the
+						-- leftovers if any.
+						any_put = true
+						inv:set_stack("main", i, existing_stack)
+						local stack_that_was_put
+						if leftover_count == 0 then
+							stack_that_was_put = stack
+						else
+							stack_that_was_put = ItemStack(stack)
+							stack_that_was_put:set_count(stack_count - leftover_count)
+						end
+						send_message(pos, "tput", stack_that_was_put, nil, i, side)
+						stack = leftover
+						stack_count = leftover_count
+						if stack_count == 0 then
+							break
+						end
+					end
+				end
 			end
-			if leftover_count ~= 0 then
+			if stack_count ~= 0 then
+				-- Walk the inventory, adding items to empty slots.
+				for i = 1, #inv_contents do
+					local existing_stack = inv_contents[i]
+					if existing_stack:is_empty() then
+						local leftover = existing_stack:add_item(stack)
+						local leftover_count = leftover:get_count()
+						if leftover_count ~= stack_count then
+							-- We put some items into the slot. Update the slot in
+							-- the inventory, tell Digilines listeners about it,
+							-- and keep looking for the a place to put the
+							-- leftovers if any.
+							any_put = true
+							inv:set_stack("main", i, existing_stack)
+							local stack_that_was_put
+							if leftover_count == 0 then
+								stack_that_was_put = stack
+							else
+								stack_that_was_put = ItemStack(stack)
+								stack_that_was_put:set_count(stack_count - leftover_count)
+							end
+							send_message(pos, "tput", stack_that_was_put, nil, i, side)
+							stack = leftover
+							stack_count = leftover_count
+							if stack_count == 0 then
+								break
+							end
+						end
+					end
+				end
+			end
+			if any_put then
+				check_full(pos, original_stack)
+			end
+			if stack_count ~= 0 then
 				-- Some items could not be added and bounced back. Report them.
-				send_message(pos, "toverflow", leftover, side)
+				send_message(pos, "toverflow", stack, nil, nil, side)
 			end
-			return leftover
+			return stack
 		end,
 		remove_items = function(pos, _, stack, dir, count)
 			-- Here, stack is the ItemStack in our own inventory that is being
@@ -147,7 +212,7 @@ minetest.register_node("digilines:chest", {
 			-- index.
 			local taken = stack:take_item(count)
 			minetest.get_meta(pos):get_inventory():set_stack("main", last_inventory_take_index, stack)
-			send_message(pos, "ttake", taken, dir)
+			send_message(pos, "ttake", taken, last_inventory_take_index, nil, dir)
 			check_empty(pos)
 			return taken
 		end,
@@ -165,6 +230,42 @@ minetest.register_node("digilines:chest", {
 		return stack:get_count()
 	end,
 	on_metadata_inventory_move = function(pos, from_list, from_index, to_list, to_index, count, player)
+		-- See what would happen if we were to move the items back from in the
+		-- opposite direction. In the event of a normal move, this must
+		-- succeed, because a normal move subtracts some items from the from
+		-- stack and adds them to the to stack; the two stacks naturally must
+		-- be compatible and so the reverse operation must succeed. However, if
+		-- the user *swaps* the two stacks instead, then due to issue
+		-- minetest/minetest#6534, this function is only called once; however,
+		-- when it is called, the stack that used to be in the to stack has
+		-- already been moved to the from stack, so we can detect the situation
+		-- by the fact that the reverse move will fail due to the from stack
+		-- being incompatible with its former contents.
+		local inv = minetest.get_meta(pos):get_inventory()
+		local from_stack = inv:get_stack("main", from_index)
+		local to_stack = inv:get_stack("main", to_index)
+		local reverse_move_stack = ItemStack(to_stack)
+		reverse_move_stack:set_count(count)
+		local swapped = from_stack:add_item(reverse_move_stack):get_count() == count
+		if swapped then
+			local channel = minetest.get_meta(pos):get_string("channel")
+			to_stack:set_count(count)
+			local msg = {
+				action = "uswap",
+				-- The slot and stack do not match because this function is
+				-- called after the action has taken place, but the Digilines
+				-- message is from the perspective of a viewer who hasn’t
+				-- observed the movement yet.
+				x_stack = to_stack:to_table(),
+				x_slot = from_index,
+				y_stack = from_stack:to_table(),
+				y_slot = to_index,
+			}
+			digilines.receptor_send(pos, digilines.rules.default, channel, msg)
+		else
+			to_stack:set_count(count)
+			send_message(pos, "umove", to_stack, from_index, to_index)
+		end
 		minetest.log("action", player:get_player_name().." moves stuff in chest at "..minetest.pos_to_string(pos))
 	end,
 	on_metadata_inventory_put = function(pos, _, index, stack, player)
@@ -196,14 +297,14 @@ minetest.register_node("digilines:chest", {
 		-- Digilines network as a utake followed by a uput.
 		local leftovers = old_stack:add_item(stack)
 		if leftovers:get_count() == stack:get_count() then
-			send_message(pos, "utake", old_stack)
+			send_message(pos, "utake", old_stack, index)
 		end
-		send_message(pos, "uput", stack)
+		send_message(pos, "uput", stack, nil, index)
 		check_full(pos, stack)
 		minetest.log("action", player:get_player_name().." puts stuff into chest at "..minetest.pos_to_string(pos))
 	end,
 	on_metadata_inventory_take = function(pos, _, index, stack, player)
-		send_message(pos, "utake", stack)
+		send_message(pos, "utake", stack, index)
 		check_empty(pos)
 		minetest.log("action", player:get_player_name().." takes stuff from chest at "..minetest.pos_to_string(pos))
 	end