augmenting unknown statement results in error

augmenting :

augment "disconnect/input" {
leaf no-remote

{ type empty; description "Do not perform this action on remote cluster node"; }

}

defined as :

grouping disconnect-grouping {
ns:action disconnect

{ description "Close all sessions to all devices."; }

}

results into error :

Error 1: Augment target 'Relative

{path=[(http://some/ns?revision=2016-01-01)disconnect, (http://some/ns?revision=2016-01-01)input]}

' not found [at null:1245:6]