GCC 4.5.2 warning: initialized field overwritten

GCC is my favourite compiler, obviously because, its open source, GPL and it  builds Linux. I prefer to use -Wall -Wextra -W -Werror options as it captures most of the bugs before in hand.

I have been working on the new XIM (extreme identity matcher) development very recently. I wanted to override the default initialization values that I gave to my struct with a local value - similar to the constructors for local objects in C++.

The code roughly looks like this.

#include 
struct A {
    int x;
    int y;
};

#define A_DEFAULTS .x = 0, .y = 0
int main(void)
{
    struct A a = {
        A_DEFAULTS,
        .y = 3
    };
    printf("a.x: %d a.y: %d\n", a.x, a.y);

    return 0;
}

The code compiles well without -W or -Wextra options. Once the extra warning flags are added, GCC starts throwing error:

04:20:38:~/Programs$ gcc 1.c -o 1 -Wall -W -Werror -std=c99
cc1: warnings being treated as errors
1.c: In function ‘main’:
1.c:23:9: error: initialized field overwritten
1.c:23:9: error: (near initialization for ‘a.y’)
04:20:43:~/Programs$ 

Totally weird. I know that this is a valid construct. Since I prefer to use -Werror switch, my code won't even compile and I'm forced to remove the switch. This may be a bug in GCC. I'm not sure. Although it won't break my design, I don't want to assign the values to my structure members after the structure members are initialized. BTW, I'm running Ubuntu 11.04 with GCC 4.5.2.

Update:

Section 6.7.8 of C99 standards clearly mentions the following about initializer list:

The initialization shall occur in initializer list order, each initializer provided for a particular subobject overriding any previously listed initializer for the same subobject; all subobjects that are not initialized explicitly shall be initialized implicitly the same as objects that have static storage duration.

Any initializer for the subobject which is overridden and so not used to initialize that subobject might not be evaluated at all.

I would like to highlight the point here:

Any initializer for the subobject which is overridden and so not used to initialize that subobject might not be evaluated at all.