Brace-initialization vs. Parenthesis Bug

I was filing a GCC bug for this, but I'd rather double-check this.

Consider the following programs:

#include <utility>
template<typename T, typename A>
void F(A&& a) { T(std::forward<A>(a)); } // Note: () syntax.
int main() { int i; F<int&>(i); }

and:

#include <utility>
template<typename T, typename A>
void F(A&& a) { T{std::forward<A>(a)}; } // Note: {} syntax.
int main() { int i; F<int&>(i); }

Latest Clang and MSVC compilers accept both programs. GCC 5 and beyond accept the first program but reject the second, claiming invalid cast of an rvalue expression of type 'int' to type 'int&'.

Is this a GCC bug? Or is this indeed a difference between T{} and T() in the above context (and thus a bug in Clang and MSVC)?