C - scanf retazca

char *a1=(char*)malloc(10*sizeof(char));
    char *a2=(char*)malloc(10*sizeof(char));

    printf("Zadaj retazec1: ");
    scanf("%9s",a1);
    printf("Zadaj retazec2: ");
    scanf("%9s",a2);

Preco mi scanf ignoruje obmedzenie nacitania poctu znakov z buffera na 9?