Spurious error log adding subscriber

[ikedas]

Version

6.2.70 (probably along with earlier versions)

Installation method

probably any

Expected behavior

Adding subscriber should not spit out error log if no errors occurred.

Actual behavior

Error (err) log is shown as following.

Nov 26 23:36:21 lists wwsympa[1067930]: info main::do_add(ikeda@conversion.co.jp) [robot sympa.community] [session 63332462411508] [client xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx] [user xxxx@xxx.xxx] [list sandbox] 
Nov 26 23:36:24 lists wwsympa[1067930]: info main::do_add(ikeda@conversion.co.jp) [robot sympa.community] [session 63332462411508] [client xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx] [xxxx@xxx.xxx] [list sandbox] 
Nov 26 23:36:24 lists wwsympa[1067930]: notice Sympa::Spindle::ProcessRequest::_twist() Processing Sympa::Request <action=add;context=sandbox@sympa.community;email=ikeda@conversion.co.jp>
Nov 26 23:36:24 lists wwsympa[1067930]: err main::#1559 > main::do_add#6969 > Sympa::Spindle::spin#95 > Sympa::Request::Handler::add::_twist#108 > Sympa::Request::Handler::add::_report_member#132 > Sympa::User::save#202 > Sympa::User::update_global_user#673 Unknown field prefs in map_field internal error

Subscriber addition itself finishes with no problem.

Steps to reproduce

Go to admin page of the list and select Users > Subscribers. Then enter email address and click "Add".

Additional information