Behavior of open is not consistent when flag O_CREAT is supplied and mode is not supplied

Code is at fd32.c:
int
w32_open(const char pathname, int flags, ... / arg /)
{
int min_index = fd_table_get_min_index();
struct w32_io pio;
va_list valist;
u_short mode = 0;

errno = 0;
if (min_index == -1)
	return -1;
if (flags & O_CREAT) {
	va_start(valist, flags);
	mode = va_arg(valist, u_short);
	va_end(valist);
}

...

following test in file_tests.c failed and commented out:
{
//f = open(tmp_filename, O_WRONLY | O_CREAT | O_TRUNC);
//ASSERT_INT_EQ(f, -1);
}

Start in fd32.c at w32_open and compare its O_CREAT argument handling with the commented test in file_tests.c. Run the relevant file tests and restore coverage for open(tmp_filename, O_WRONLY | O_CREAT | O_TRUNC) without a mode argument; done means the behavior is consistent and the test passes.