Event subscription mode Stateless does not work?

While doing !906 (merged) I found, that stateless=True and submode=EventSubMode.Stateless work differntly.

We use it in this test: https://gitlab.com/tango-controls/pytango/-/blob/0701e772c37ebcee125c3de865d566d3cb6d2a12/tests/test_device_proxy.py#L783

And when I tried to use submode=EventSubMode.Stateless ti avoid warning, test does not work: https://gitlab.com/tango-controls/pytango/-/jobs/11475634118#L2580