Command_inout_asynch empty argout

I try to execute command_inout_asynch in PyTango client, but every time I've got an event with empty argout (and argout_raw). All other fields of the event are correct, e.g. event.device

Code example:

import PyTango
import time

class TestClass():

    def __init__(self):

        api_util = PyTango.ApiUtil.instance()
        # change client to "push" model
        api_util.set_asynch_cb_sub_model(PyTango.cb_sub_model.PUSH_CALLBACK) 
        self.dev = PyTango.DeviceProxy('sys/tg_test/1')

    def cmd(self):
        self.dev.command_inout_asynch('Status', self.callback)
        time.sleep(0.5)  # not immediate response, have to wait some time

    def callback(self, event):
        print(event)
        print(event.device)
        print(event.argout)
        print(event.argout_raw)

def main():

    test = TestClass()
    test.cmd()

if __name__ == '__main__':
    main()

Console output:

<tango._tango.CmdDoneEvent object at 0x04344CA8>
TangoTest(sys/tg_test/1)
None
DeviceData[
]

The problem replicates both on Windows and Linux, Python 2.7 and 3.4, Pytango 9.2.0 and 9.2.2.

P.S.: Also documentation about all kinds of "command_inout" dissapearred from http://pytango.readthedocs.io/en/latest/contents.html