C++11 strange brace initialization behavior

Question

I don't understand how C++11 brace initialization rules work here. Having this code:

struct Position_pod {     int x,y,z; };  class Position { public:     Position(int x=0, int y=0, int z=0):x(x),y(y),z(z){}     int x,y,z; };  struct text_descriptor {     int             id;     Position_pod    pos;     const int       &constNum; };  struct text_descriptor td[3] = {      {0, {465,223}, 123},      {1, {465,262}, 123}, };  int main()  {     return 0; } 

Note, that the array is declared to have 3 elements, but only 2 initializers are provided.

However it compiles without error, which sounds strange, as the last array element's reference member will be uninitialized. Indeed, it has NULL value:

(gdb) p td[2].constNum  $2 = (const int &) @0x0: <error reading variable> 

And now the "magic": I changed Position_pod to Position

struct text_descriptor {     int             id;     Position_pod    pos;     const int       &constNum; }; 

becomes this:

struct text_descriptor {     int             id;     Position        pos;     const int       &constNum; }; 

and now it gives the expected error:

error: uninitialized const member ‘text_descriptor::constNum' 

My question: Why it compiles in the first case, when it should give an error (as in the second case). The difference is, that Position_pod uses C - style brace initialization and Position uses C++11 - style initialization, which call Position's constructor. But how does this affect the possibility to leave a reference member uninitialized?

(Update) Compiler: gcc (Ubuntu 4.8.2-19ubuntu1) 4.8.2