How does an array of structures with flexible array members behave?

As the title states I was wondering how arrays of C-structs with a flexible array member behaves. Here is an example:

struct vector {
    size_t length;
    double array[];
};

The Wikipedia article says:

The sizeof operator on such a struct is required to give the offset of the flexible array member.

On my machine this corresponds to 8 bytes (sizeof(size_t)). But what happens, when I do the following:

Obviously the array cannot hold the data of vector v0, since it's only 3*8 bytes = 24 bytes wide. How can I deal with situations like this?

#define LENGTH 10

int main() {
    struct vector arr[3];

    struct vector *v0 = calloc(1, sizeof(*v0) + LENGTH * sizeof(v0->array[0]));
    v0->length = LENGTH;

    size_t i;
    for (i = 0; i < v0->length; i++) {
        v0->array[i] = (double) i;
    }

    struct vector v1;
    struct vector v2;

    arr[0] = *v0;
    arr[1] =  v1;
    arr[2] =  v2;

    for (i = 0; i < arr[0].length; i++) {
        printf("arr[0].array[%2zu] equals %2.0lf.\n", i, arr[0].array[i]);
        printf("    v0->data[%2zu] equals %2.0lf.\n", i, v0->array[i]);
    }
    return 0;
}

For example, when I'm writing a library (header: mylib.h, source: my lib.c) and want to hide the implementation of one specific struct from the user (struct declared in header, defined in source - hidden). Sadly exactly this struct contains a flexible array member. Won't this lead to unexpected behavior, when the user tries to create an array of named structures?

Extra: Read more about the flexible array in the OpenSTD C Spec.
Just search for 'flexible array member'.

EDIT: The latest draft of the C11 Standard, the most up to date freely available reference for the C language is available here: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf