why foo2 is not inferred as scope which is shorter scope then foo1?

import std.stdio;

@safe:

class Obj {@safe: override string toString() { return "obj"; } }

struct Foo1
{@safe:
    this(Obj obj) { this._obj = obj; }
    ~this() { _obj = null; } // do something with obj
    // _obj must not be out live with Foo1, so need return attribute
    @property Obj obj() return { return _obj; }
    private Obj _obj;
}

struct Foo2
{@safe:
    this(Obj obj) { this._obj = obj; }
    ~this() { _obj = null; } // do something with obj
    void call() { writeln(_obj.toString()); }
    // _obj must not be out live with Foo1, so need return attribute
    @property Obj obj() return { return _obj; }
    private Obj _obj;
}

void call1() { auto obj = new Obj(); auto foo1 = Foo1(obj); call2(foo1); }

// foo2 borrows foo1.obj and do something with it
void call2(ref Foo1 foo1) { auto foo2 = Foo2(foo1.obj); call3(foo2); }

void call3(ref Foo2 foo2) { foo2.call(); }

void main() { call1(); }

Getting below error message
onlineapp.d(29): Error: reference to local variable foo1 assigned to non-scope parameter obj calling onlineapp.Foo2.this

Remove "return" from property obj fix the error message