write_attribute_asynch() incomplete error stack

The following code (using pytango 10.1.1):

ds = tango.DeviceProxy("srmag/m-qf1/c03-a") 
ds.write_attribute("strength",100.0)

returns the correct error stack:

tango._tango.DevFailed: DevFailed[
    DevError[
        desc = srmag/vps-qf1/c03-a:35111.796257 not in [0.000000..110.000000]
        origin = Magnet::check_minmax
        reason = SetpointCheckError
        severity = ERR
    ],
    DevError[
        desc = Failed to write_attribute on device srmag/m-qf1/c03-a, attribute strength
        origin = virtual void Tango::DeviceProxy::write_attribute(const Tango::DeviceAttribute&) at (/src/cppTango/src/client/devapi_base.cpp:7056)
        reason = API_AttributeFailed
        severity = ERR

]

]

while the code bellow:

ds = tango.DeviceProxy("srmag/m-qf1/c03-a")
attr_config = ds.get_attribute_config("strength")
asynch_call_id = ds.write_attribute_asynch(attr_config, 100.0)
ds.write_attribute_reply(asynch_call_id,3000)

returns an incomplete error stack:

tango._tango.DevFailed: DevFailed[
    DevError[
        desc = Failed to execute DeviceProxy::write_attributes_reply() on device srmag/m-qf1/c03-a, object(s) Strength
        origin = DeviceProxy::write_attributes_reply()
        reason = API_AttributeFailed
        severity = ERR
    ]
]