Strange Metamethod Behavior

[paulevsGitch]

LuaCSharp version: 0.5.0

During testing metamethods I found some weird behavior. If metamethod (for example adding) is defined inside C# object then it has a huge chance to fail in the Lua (sometimes method is not called at all). If it is assigning to a new local then method is not called and local became nil, if it is assigning to one of created object then result is successful.

Here is an example C# class:

[LuaObject]
public partial class LuaTestObj {
	private float x;
	private float y;

	[LuaMember("x")]
	public float X {
		get => x;
		set => x = value;
	}

	[LuaMember("y")]
	public float Y {
		get => y;
		set => y = value;
	}

	[LuaMember("create")]
	public static LuaTestObj Create(float x, float y) {
		return new LuaTestObj() {
			x = x,
			y = y
		};
	}

	[LuaMetamethod(LuaObjectMetamethod.Add)]
	public static LuaTestObj Add(LuaTestObj a, LuaTestObj b) {
		return new LuaTestObj() {
			x = a.x + b.x,
			y = a.y + b.y
		};
	}

	[LuaMetamethod(LuaObjectMetamethod.ToString)]
	public override string ToString() {
		return $"({x}, {y})";
	}
}

And an example of Lua code with output:

local a = TestObj.create(1, 2)
local b = TestObj.create(3, 4)

print("a ->", tostring(a)) -- prints (1, 2)
print("b ->", tostring(b)) -- prints (3, 4)
print()

local c = a + b

print("c ->", tostring(c)) -- prints nil, __add is not called
print("a + b ->", tostring(a + b)) -- prints nil, __add is not called
print()

a = a + b
print("a ->", tostring(a)) -- prints (4, 6), __add is called

However if the same object is defined on Lua side:

TestObj = {
	mt = {
		__add = function (a, b)
			return TestObj.create(a.x + b.x, a.y + b.y)
		end,
		__tostring = function (a)
			return "(" .. a.x .. ", " .. a.y .. ")"
		end
	},
	create = function (x, y)
		local obj = {
			x = x,-- | 0.0,
			y = y -- | 0.0
		}
		setmetatable(obj, TestObj.mt)
		return obj
	end
}

The results are always correct:

I'm not sure if this is a bug or I'm doing something incorrectly.