diff --git a/src/itemstackmetadata.cpp b/src/itemstackmetadata.cpp
index be1715e1a..a2fc67c46 100644
--- a/src/itemstackmetadata.cpp
+++ b/src/itemstackmetadata.cpp
@@ -89,11 +89,11 @@ void ItemStackMetadata::deSerialize(std::istream &is)
 			while (!fnd.at_end()) {
 				std::string name = fnd.next(DESERIALIZE_KV_DELIM_STR);
 				std::string var  = fnd.next(DESERIALIZE_PAIR_DELIM_STR);
-				m_stringvars[name] = var;
+				m_stringvars[name] = std::move(var);
 			}
 		} else {
 			// BACKWARDS COMPATIBILITY
-			m_stringvars[""] = in;
+			m_stringvars[""] = std::move(in);
 		}
 	}
 	updateToolCapabilities();
diff --git a/src/nodemetadata.cpp b/src/nodemetadata.cpp
index a11503ebe..a86db15ad 100644
--- a/src/nodemetadata.cpp
+++ b/src/nodemetadata.cpp
@@ -62,14 +62,14 @@ void NodeMetadata::serialize(std::ostream &os, u8 version, bool disk) const
 void NodeMetadata::deSerialize(std::istream &is, u8 version)
 {
 	clear();
-	int num_vars = readU32(is);
-	for(int i=0; i<num_vars; i++){
+	u32 num_vars = readU32(is);
+	for (u32 i = 0; i < num_vars; i++){
 		std::string name = deSerializeString16(is);
 		std::string var = deSerializeString32(is);
-		m_stringvars[name] = var;
+		m_stringvars[name] = std::move(var);
 		if (version >= 2) {
 			if (readU8(is) == 1)
-				markPrivate(name, true);
+				m_privatevars.insert(name);
 		}
 	}
 
@@ -89,12 +89,12 @@ bool NodeMetadata::empty() const
 }
 
 
-void NodeMetadata::markPrivate(const std::string &name, bool set)
+bool NodeMetadata::markPrivate(const std::string &name, bool set)
 {
 	if (set)
-		m_privatevars.insert(name);
+		return m_privatevars.insert(name).second;
 	else
-		m_privatevars.erase(name);
+		return m_privatevars.erase(name) > 0;
 }
 
 int NodeMetadata::countNonPrivate() const
@@ -144,6 +144,8 @@ void NodeMetadataList::serialize(std::ostream &os, u8 blockver, bool disk,
 			writeS16(os, p.Z);
 		} else {
 			// Serialize positions within a mapblock
+			static_assert(MAP_BLOCKSIZE * MAP_BLOCKSIZE * MAP_BLOCKSIZE <= U16_MAX,
+				"position too big to serialize");
 			u16 p16 = (p.Z * MAP_BLOCKSIZE + p.Y) * MAP_BLOCKSIZE + p.X;
 			writeU16(os, p16);
 		}
@@ -246,8 +248,7 @@ void NodeMetadataList::set(v3s16 p, NodeMetadata *d)
 void NodeMetadataList::clear()
 {
 	if (m_is_metadata_owner) {
-		NodeMetadataMap::const_iterator it;
-		for (it = m_data.begin(); it != m_data.end(); ++it)
+		for (auto it = m_data.begin(); it != m_data.end(); ++it)
 			delete it->second;
 	}
 	m_data.clear();
diff --git a/src/nodemetadata.h b/src/nodemetadata.h
index da277aabd..3c2a67f53 100644
--- a/src/nodemetadata.h
+++ b/src/nodemetadata.h
@@ -57,7 +57,10 @@ public:
 	{
 		return m_privatevars.count(name) != 0;
 	}
-	void markPrivate(const std::string &name, bool set);
+
+	/// Marks a key as private.
+	/// @return metadata modified?
+	bool markPrivate(const std::string &name, bool set);
 
 private:
 	int countNonPrivate() const;
diff --git a/src/script/lua_api/l_itemstackmeta.cpp b/src/script/lua_api/l_itemstackmeta.cpp
index ebabf7bae..730fab3b4 100644
--- a/src/script/lua_api/l_itemstackmeta.cpp
+++ b/src/script/lua_api/l_itemstackmeta.cpp
@@ -41,7 +41,7 @@ void ItemStackMetaRef::clearMeta()
 
 void ItemStackMetaRef::reportMetadataChange(const std::string *name)
 {
-	// TODO
+	// nothing to do
 }
 
 // Exported functions
@@ -89,7 +89,6 @@ ItemStackMetaRef::~ItemStackMetaRef()
 void ItemStackMetaRef::create(lua_State *L, LuaItemStack *istack)
 {
 	ItemStackMetaRef *o = new ItemStackMetaRef(istack);
-	//infostream<<"NodeMetaRef::create: o="<<o<<std::endl;
 	*(void **)(lua_newuserdata(L, sizeof(void *))) = o;
 	luaL_getmetatable(L, className);
 	lua_setmetatable(L, -2);
@@ -98,9 +97,6 @@ void ItemStackMetaRef::create(lua_State *L, LuaItemStack *istack)
 void ItemStackMetaRef::Register(lua_State *L)
 {
 	registerMetadataClass(L, className, methods);
-
-	// Cannot be created from Lua
-	//lua_register(L, className, create_object);
 }
 
 const char ItemStackMetaRef::className[] = "ItemStackMetaRef";
diff --git a/src/script/lua_api/l_nodemeta.cpp b/src/script/lua_api/l_nodemeta.cpp
index f1a2d5c4b..07bdced99 100644
--- a/src/script/lua_api/l_nodemeta.cpp
+++ b/src/script/lua_api/l_nodemeta.cpp
@@ -58,6 +58,8 @@ void NodeMetaRef::reportMetadataChange(const std::string *name)
 	// Inform other things that the metadata has changed
 	NodeMetadata *meta = dynamic_cast<NodeMetadata*>(getmeta(false));
 
+	bool is_private_change = meta && name && meta->isPrivate(*name);
+
 	// If the metadata is now empty, get rid of it
 	if (meta && meta->empty()) {
 		clearMeta();
@@ -67,7 +69,7 @@ void NodeMetaRef::reportMetadataChange(const std::string *name)
 	MapEditEvent event;
 	event.type = MEET_BLOCK_NODE_METADATA_CHANGED;
 	event.setPositionModified(m_p);
-	event.is_private_change = name && meta && meta->isPrivate(*name);
+	event.is_private_change = is_private_change;
 	m_env->getMap().dispatchEvent(event);
 }
 
@@ -94,21 +96,24 @@ int NodeMetaRef::l_mark_as_private(lua_State *L)
 
 	NodeMetaRef *ref = checkObject<NodeMetaRef>(L, 1);
 	NodeMetadata *meta = dynamic_cast<NodeMetadata*>(ref->getmeta(true));
-	assert(meta);
+	if (!meta)
+		return 0;
 
+	bool modified = false;
 	if (lua_istable(L, 2)) {
 		lua_pushnil(L);
 		while (lua_next(L, 2) != 0) {
 			// key at index -2 and value at index -1
 			luaL_checktype(L, -1, LUA_TSTRING);
-			meta->markPrivate(readParam<std::string>(L, -1), true);
+			modified |= meta->markPrivate(readParam<std::string>(L, -1), true);
 			// removes value, keeps key for next iteration
 			lua_pop(L, 1);
 		}
 	} else if (lua_isstring(L, 2)) {
-		meta->markPrivate(readParam<std::string>(L, 2), true);
+		modified |= meta->markPrivate(readParam<std::string>(L, 2), true);
 	}
-	ref->reportMetadataChange();
+	if (modified)
+		ref->reportMetadataChange();
 
 	return 0;
 }
@@ -145,12 +150,13 @@ bool NodeMetaRef::handleFromTable(lua_State *L, int table, IMetadata *_meta)
 	Inventory *inv = meta->getInventory();
 	lua_getfield(L, table, "inventory");
 	if (lua_istable(L, -1)) {
+		auto *gamedef = getGameDef(L);
 		int inventorytable = lua_gettop(L);
 		lua_pushnil(L);
 		while (lua_next(L, inventorytable) != 0) {
 			// key at index -2 and value at index -1
-			std::string name = luaL_checkstring(L, -2);
-			read_inventory_list(L, -1, inv, name.c_str(), getServer(L));
+			const char *name = luaL_checkstring(L, -2);
+			read_inventory_list(L, -1, inv, name, gamedef);
 			lua_pop(L, 1); // Remove value, keep key for next iteration
 		}
 		lua_pop(L, 1);
@@ -177,7 +183,6 @@ NodeMetaRef::NodeMetaRef(IMetadata *meta):
 void NodeMetaRef::create(lua_State *L, v3s16 p, ServerEnvironment *env)
 {
 	NodeMetaRef *o = new NodeMetaRef(p, env);
-	//infostream<<"NodeMetaRef::create: o="<<o<<std::endl;
 	*(void **)(lua_newuserdata(L, sizeof(void *))) = o;
 	luaL_getmetatable(L, className);
 	lua_setmetatable(L, -2);
diff --git a/src/script/lua_api/l_playermeta.cpp b/src/script/lua_api/l_playermeta.cpp
index e2e6ed8da..e937c145c 100644
--- a/src/script/lua_api/l_playermeta.cpp
+++ b/src/script/lua_api/l_playermeta.cpp
@@ -38,7 +38,7 @@ void PlayerMetaRef::clearMeta()
 
 void PlayerMetaRef::reportMetadataChange(const std::string *name)
 {
-	// TODO
+	// the server saves these on its own
 }
 
 // Creates an PlayerMetaRef and leaves it on top of stack
@@ -54,9 +54,6 @@ void PlayerMetaRef::create(lua_State *L, IMetadata *metadata)
 void PlayerMetaRef::Register(lua_State *L)
 {
 	registerMetadataClass(L, className, methods);
-
-	// Cannot be created from Lua
-	// lua_register(L, className, create_object);
 }
 
 const char PlayerMetaRef::className[] = "PlayerMetaRef";