Why does this snippet using uniform initialization compile with g++4.6 but not g++4.7?

Note that derived uses C++11 uniform initialization syntax to call the base class constructor.

class base
{
    protected:
        base()
        {}
};

class derived : public base
{
    public:
        derived()
            : base{} // <-- Note the c++11 curly brace syntax
                     // using uniform initialization. Change the
                     // braces to () and it works.
        {}
};

int main()
{
    derived d1;

    return 0;
}

g++4.6 compiles this, however g++4.7 does not:

$ g++-4.7 -std=c++11 -Wall -Wextra -pedantic curly.cpp -o curly
curly.cpp: In constructor ‘derived::derived()’:
curly.cpp:4:13: error: ‘base::base()’ is protected
curly.cpp:19:24: error: within this context

What's going on?

Update 1: It also compiles without warnings with clang++-3.1
Update 2: Looks like a compiler bug for sure. It's apparently fixed in GCC 4.7.3.

Paolo Carlini, a GCC/libstdc++ contributor, confirmed it is a bug/regression.