program for which the octagon domain is less precise than integer domain

interesting.c

int __VERIFIER_nondet_int();
extern void __VERIFIER_error() __attribute__((noreturn));

void __VERIFIER_assert(int cond) {
    if (!cond) {
    ERROR: __VERIFIER_error();
    }
}

int main()
{
    int q = 0;
    int method_id;
    unsigned int this_expect = 0;
    unsigned int this_buffer_empty = 0;
    while (1)
    {
        int P1 = __VERIFIER_nondet_int();
        int P3 = __VERIFIER_nondet_int();
        int P4 = __VERIFIER_nondet_int();
        int P6 = __VERIFIER_nondet_int();
        if (q == 0)
        {
            if (__VERIFIER_nondet_int())
            {
                    method_id = 1;
                    q = 1;
                    this_expect = 0;
                    this_buffer_empty = 1;
                continue;
            }
            continue;
        }
        if (q == 1)
        {
            if (__VERIFIER_nondet_int())
            {
                if (!(P1 % 2 != 0 % 2))
                {
                    method_id = 2;
                    if (P1 % 2 != this_expect % 2 && this_buffer_empty == 1 && !(P1 % 2 != 0 % 2) || this_buffer_empty != 1 && !(P1 % 2 != 0 % 2))
                    {
                        ;
                    }

                    q = 3;
                    this_expect = this_expect + 1;
                    this_buffer_empty = 1 - this_buffer_empty;
                }
                continue;
            }
            if (__VERIFIER_nondet_int())
            {
                if (!(P1 != (0 + 1 - 1) % 2))
                {
                    method_id = 3;
                    if (P3 == (this_expect - 1) % 2 && this_buffer_empty != 1 && !(P3 != (0 + 1 - 1) % 2))
                    {
                        ;
                    }
                    q = 2;
                    break;
                }
                continue;
            }
            if (__VERIFIER_nondet_int())
            {
                if (P1 % 2 != 0 % 2 && (P1 % 2 != (0 + 1) % 2 && P1 % 2 != 0 % 2))
                {
                    method_id = 4;
                    if (P4 % 2 == this_expect % 2 && this_buffer_empty == 1 && P4 % 2 != 0 % 2 && (P4 % 2 != 0 % 2 && (P4 % 2 != (0 + 1) % 2 && P4 % 2 != 0 % 2)))
                    {
                        ;
                    }
                    q = 2;
                    break;
                }
                continue;
            }
            if (__VERIFIER_nondet_int())
            {
                if (P1 % 2 != 0 % 2 && !(P1 % 2 != (0 + 1) % 2 && P1 % 2 != 0 % 2))
                {
                    method_id = 5;
                    if (P6 % 2 == this_expect % 2 && this_buffer_empty == 1 && P6 % 2 != 0 % 2 && (P6 % 2 != 0 % 2 && !(P6 % 2 != (0 + 1) % 2 && P6 % 2 != 0 % 2)))
                    {
                        ;
                    }
                    q = 2;
                    break;
                }
                continue;
            }
            /* do not remove this */
            if (__VERIFIER_nondet_int())
            {
                continue;
            }
            continue;
        }
        __VERIFIER_assert(q != 1);
    }
    return 0;
}