guest_delete_disks failed to delete unexist disk

Here is the response, userid vroplu02 is logged on, and disk 4000 not exist

>>> c.send_request('guest_delete_disks', 'vroplu02', ['4000'])
{u'rs': 1, u'overallRC': 2, u'modID': 1, u'rc': 8, u'output': u'', u'errmsg': u'Failed to remove disk with vdev \'4000\' from userid \'VROPLU02\'. SMUT error: SMUT request failed. RequestData: \'changevm VROPLU02 removedisk 4000\', Results: \'{\'rs\': 1, \'errno\': 0, \'strError\': \'\', \'overallRC\': 2, \'rc\': 8, \'response\': [\'(Error) ULTVMU0316E On VROPLU02, command sent through IUCV failed. cmd: /sbin/vmcp detach 4000, rc: 8, rs: 1, out: ERROR: HCPDTV040E Device 4000 does not exist\', "Error: non-zero CP response for command \'DETACH 4000\': #40", \'\', \'Return code 8, Reason code 1.\']}\''}