It works!

worldeditadditions/lib/subdivide.lua

@@ -51,13 +51,13 @@ end
 
 local function subdivide_step_beforeload(state)
 	state.cpos.z = state.cpos.z - (state.chunk_size.z + 1)
-	if state.cpos.z <= state.pos1.z then
+	if state.cpos.z < state.pos1.z then
 		state.cpos.z = state.pos2.z
 		state.cpos.y = state.cpos.y - (state.chunk_size.y + 1)
-		if state.cpos.y <= state.pos1.y then
+		if state.cpos.y < state.pos1.y then
 			state.cpos.y = state.pos2.y
 			state.cpos.x = state.cpos.x - (state.chunk_size.x + 1)
-			if state.cpos.x <= state.pos1.x then
+			if state.cpos.x < state.pos1.x then
 				subdivide_step_complete(state)
 				return
 			end
@@ -125,6 +125,7 @@ end
 -- @param	{function}	callback	The callback to call upon completion.
 function worldeditadditions.subdivide(pos1, pos2, chunk_size, callback_subblock, callback_complete)
 	pos1, pos2 = worldedit.sort_pos(pos1, pos2)
+	local chunks_total = count_chunks(pos1, pos2, chunk_size)
 	
 	chunk_size.x = chunk_size.x - 1 -- WorldEdit regions are inclusive
 	chunk_size.y = chunk_size.y - 1 -- WorldEdit regions are inclusive
@@ -132,7 +133,8 @@ function worldeditadditions.subdivide(pos1, pos2, chunk_size, callback_subblock,
 	
 	local state = {
 		pos1 = pos1, pos2 = pos2,
-		cpos = { x = pos2.x, y = pos2.y, z = pos2.z },
+		-- Note that we start 1 over on the Z axis because we increment *before* calling the callback, so if we don't fiddle it here, we'll miss the first chunk
+		cpos = { x = pos2.x, y = pos2.y, z = pos2.z + chunk_size.z + 1 },
 		-- The size of a single subblock
 		chunk_size = chunk_size,
 		-- The total number of nodes in the defined region
@@ -153,7 +155,7 @@ function worldeditadditions.subdivide(pos1, pos2, chunk_size, callback_subblock,
 		-- The percentage of the total time spent so far waiting for Minetest to emerge blocks. Updated every step.
 		emerge_overhead = 0,
 		-- The total number of chunks
-		chunks_total = count_chunks(pos1, pos2, chunk_size),
+		chunks_total = chunks_total,
 		-- The number of chunks processed so far
 		chunks_completed = 0,
 		callback_subblock = callback_subblock,

worldeditadditions_commands/commands/meta/subdivide.lua

@@ -22,7 +22,9 @@ end
 local function emerge_stats_tostring(tbl_emerge)
 	local result = {}
 	for key,value in pairs(tbl_emerge) do
-		table.insert(result, string.format("%s=%d", key, value))
+		if value > 0 then
+			table.insert(result, string.format("%s=%d", key, value))
+		end
 	end
 	return table.concat(result, ", ")
 end
@@ -99,6 +101,7 @@ worldedit.register_command("subdivide", {
 			worldedit.player_notify_suppress(name)
 			worldedit.pos1[name] = cpos1
 			worldedit.pos2[name] = cpos2
+			worldedit.marker_update(name)
 			cmd.func(name, args)
 			if will_trigger_saferegion(name, cmd_name, args) then
 				minetest.chatcommands["/y"].func()
@@ -121,8 +124,12 @@ worldedit.register_command("subdivide", {
 				time_last_msg = wea.get_ms_time()
 			end
 		end, function(_, _, stats)
+			worldedit.pos1[name] = pos1
+			worldedit.pos2[name] = pos2
+			worldedit.marker_update(name)
+			
 			-- Called on completion
-			minetest.log("action", string.format("%s used //subdivide at %s - %s, with $d chunks and %d total nodes in %s",
+			minetest.log("action", string.format("%s used //subdivide at %s - %s, with %d chunks and %d total nodes in %s",
 				name,
 				wea.vector.tostring(pos1),
 				wea.vector.tostring(pos2),
@@ -130,15 +137,16 @@ worldedit.register_command("subdivide", {
 				stats.volume_nodes,
 				wea.human_time(stats.times.total)
 			))
-			return true, string.format(
+			worldedit.player_notify(name, string.format(
 				"%sComplete: %d chunks processed in %s (%.2f%% emerge overhead, emerge totals: %s)",
 				msg_prefix,
 				stats.chunks_completed,
-				wea.human_time(stats.time.total),
+				wea.human_time(stats.times.total),
 				stats.emerge_overhead * 100,
 				emerge_stats_tostring(stats.emerge)
-			)
+			))
 		end)
 		
+		return true
 	end
 })