Reduced from http://stackoverflow.com/q/38213809/2756719. Repro:

class Meow
{
  protected:
    Meow() =default;        
    virtual void f() {}
};

class Purr : public Meow
{
  public:
    Purr()
      : Meow{}
    {}  
};

prog.cc: In constructor 'Purr::Purr()':
prog.cc:12:14: error: 'constexpr Meow::Meow()' is protected within this context
       : Meow{}
              ^
prog.cc:4:5: note: declared protected here
     Meow() =default;
     ^~~~

Possibly related to PR63151, however this example reproduces in GCC 4.7.3 and 4.8.5 (on Wandbox), while that PR is known to work in 4.8.2.