Defaulted, explicitly noexcept destructor is not noexcept

Question

I am on GCC version 8.1.0, and am using the type trait std::is_nothrow_default_constructible_v to check for throwing destructors (the implementation happens to be using noexcept() to check for non throwing constructors).

However, I have stumbled upon an interesting phenomenon that might be a compiler bug. I'm asking here for confirmation; here is the minimal reproducible example:

#include <type_traits>

struct B {
    ~B() noexcept(false) {}
};

struct A {
    B b;
    ~A() noexcept = default;
};


int main()
{
    static_assert(std::is_nothrow_default_constructible_v<A>);
    return 0;
}

Note that if i do ~A() noexcept {} instead of ~A() noexcept = default;, the code compiles as expected.

What is happening here?