LinkedIn, Undefined index: user in social_login_core_form_user_register_form_alter() (line 864 of social_login_core.module)

* Checked that I can login to my [own site](http://support.netgenius.co.uk) using LinkedIn - Yes, so there's no fundamental problem at LinkedIn (that login uses *HybridAuth* module, not *OneAll*).
* Tried to use log in with LinkedIn using Social Login - no error message, redirected to *user/register* and social login icons are no longer displayed login/register pages (clearing *sessions* makes them come back).
* Message in watchdog log: *Notice: Undefined index: user in social_login_core_form_user_register_form_alter() (line 864 of /data/www2/clones/scientist_solutions/scientist-solutions.pantheon/sites/all/modules/social_login/social_login_core.module)* (repeated several times).
* Data from the response, *$social_data*, printed just after line #251 in *social_login_core.module*:

$social_data => Array
(
    [response] => Array
        (
            [request] => Array
                (
                    [date] => Tue, 01 Dec 2015 12:01:50 +0100
                    [resource] => /connections/35eb19aa-53ef-4411-afd3-cec18de7ba86.json
                    [status] => Array
                        (
                            [flag] => success
                            [code] => 200
                            [info] => Your request has been processed successfully
                        )

                )

            [result] => Array
                (
                    [status] => Array
                        (
                            [flag] => error
                            [code] => 401
                            [info] => The user did not authenticate successfully
                        )

                    [data] => Array
                        (
                            [action] => authenticate_user
                            [plugin] => Array
                                (
                                    [key] => social_login
                                    [data] => Array
                                        (
                                            [action] => login
                                            [operation] => nothing_to_do
                                            [reason] => user_cancelled
                                            [status] => error
                                        )

                                )

                            [connection] => Array
                                (
                                    [connection_token] => 35eb19aa-53ef-4411-afd3-cec18de7ba86
                                    [date] => Tue, 01 Dec 2015 12:01:49 +0100
                                )

                        )

                )

        )

)

This is consistently repeatable. Quite possibly I don't have the LinkedIn side properly configured, but in any case Social Login module is ignoring the 401 error in [response][result][status][code]