为什么调用这个复制构造函数而不是移动构造函数?

The following code snippet causes the copy constructor to be called where I expected the move constructor to be called:

#include <cstdio>

struct Foo
{
    Foo() { puts("Foo gets built!"); }
    Foo(const Foo& foo) { puts("Foo gets copied!"); }
    Foo(Foo&& foo) { puts("Foo gets moved!"); }
};

struct Bar { Foo foo; };
Bar Meow() { Bar bar; return bar; }
int main() { Bar bar(Meow()); }

在 VS11 Beta 上，在调试模式下，打印:

Foo gets built!
Foo gets copied!
Foo gets copied!