is the locking broken in free threaded python version?

# try this with Python 3.15.0b1 and 3.15.0b1t
# the freethreaded version looses results
# if time.sleep(0) is removed, it's even worse
# the non-freethreaded version does not have this issue


import time
from threading import Thread, synchronized_iterator
from itertools import batched

@synchronized_iterator
def numbers(n):
    for x in range(n):
        yield x

def consume(iterable, results):
    numbers_append = results.append
    for item in iterable:
        numbers_append(item)
        time.sleep(0)

def is_ok(numbers):
    for batch in batched(numbers, 2):
        if len(batch) == 2:
            last, current = batch
        else:
            # handling odd length of numbers
            last, current = current, batch[0]

        if last + 1 != current:
            return False

    return True


THREADS = 2
success = 0
errors = 0
all_results = []

for try_number in range(100):
    print(f"Try number: {try_number + 1}")
    results = []
    all_results.append(results)
    gen = numbers(1_001)
    threads = [Thread(target=consume, args=(gen, results)) for _ in range(THREADS)]
    for t in threads:
        t.start()
    for t in threads:
        t.join()

    if is_ok(results):
        success += 1
    else:
        errors += 1

print(f"{success} times success and {errors} errors")