lua 5.4 __close and collectgarbage causes crash

I have Lua 5.4 embedded in a project and implemented __close metamethod for a userdata, which is a vector of numbers. The project has its own script editor and is able to run the scripts. The implementation of __close is exactly the same as __gc metamethod, which is shown below:

int Vector_gc(lua_State* L)
{
    CVector<double>* vector = *(CVector<double>**)lua_touserdata(L, 1);

    delete vector;

    return 0;
}

1) In a script file, when running the following script, there is no problem at all:

local vector=std.rand(5000) --generate 5000 random numbers
vector=nil

collectgarbage()

2) Similarly, if I run the following script file more than once, again no problem at all:

local vector <close> = std.rand(5000)

3) However, the following script using collectgarbage when run more than once causes crash:

local vector <close> = std.rand(5000)

collectgarbage()

EDIT 1:

4) The following causes an immediate crash.

if(true) then
    local vector <close> = std.rand(5000)
    vector[2]=1
end

collectgarbage()

Am I misunderstanding/missing something about to-be-closed variables?