Does that make sense? feature or bug?

void main(){

  import std.algorithm;

  import std.array;

  {

    int counter=0;

    auto b=[1,2,3].map!(a=>{counter++; return [a];}()).joiner([0]).array;

    assert(counter==3);

  }

  {

    int counter=0;

    auto b=[1,2,3].map!(a=>{counter++; return [a];}()).joiner().array;

    assert(counter==6);//why 6 whereas other one was 3?

  }

}