ProcessPoolExecutorの中断は他のと違う

以下のコードはmax_workersを1にしてExecutorを作り、2つ仕事を与えて1つ目が終わる前に2つ目に中断を試みるものです。

import pytest

from concurrent.futures import ProcessPoolExecutor, ThreadPoolExecutor, InterpreterPoolExecutor


@pytest.mark.parametrize(
    "executor_cls",
    (ProcessPoolExecutor, ThreadPoolExecutor, InterpreterPoolExecutor)
)
def test_cancel_before_start_executing(executor_cls):
    import time

    with executor_cls(max_workers=1) as executor:
        executor.submit(time.sleep, 2)  # １つ目の仕事
        time.sleep(.5)
        fut = executor.submit(time.sleep, 1)  # ２つ目の仕事
        time.sleep(.5)
        assert fut.cancel()  # 中断

==================================================================== FAILURES ====================================================================
____________________________________________ test_cancel_before_start_executing[ProcessPoolExecutor] _____________________________________________

executor_cls = <class 'concurrent.futures.process.ProcessPoolExecutor'>

    @pytest.mark.parametrize(
        "executor_cls",
        (ProcessPoolExecutor, ThreadPoolExecutor, InterpreterPoolExecutor)
    )
    def test_cancel_before_start_executing(executor_cls):
        import time
    
        with executor_cls(max_workers=1) as executor:
            executor.submit(time.sleep, 2)
            time.sleep(.5)
            fut = executor.submit(time.sleep, 1)
            time.sleep(.5)
>           assert fut.cancel()
E           assert False
E            +  where False = cancel()
E            +    where cancel = <Future at 0x7d59d31be5d0 state=running>.cancel

ProcessPoolExecutorだけが中断に失敗してしまいました。ただ以下のようにsubmitの直後に中断を試みた場合はどのExecutorでもうまく行きました。

         fut = executor.submit(time.sleep, 1)
+        assert fut.cancel()
         time.sleep(.5)
-        assert fut.cancel()

環境

• CPython 3.14.5
• pytest 9.0.3