As reported:
Contrary to the documentation, $wgRateLimits entry for 'user' overrides that for 'newbie'.
For example, with the following configuration, newly registered accounts are able to edit 10 pages per hour instead of 5:
$wgRateLimits[ 'edit' ] = [
'user' => [ 10, 60*60 ],
'newbie' => [ 5, 60*60 ],
];
This seems to be the opposite of what documentation in DefaultSettings.php says:
'newbie' => [ x, y ], // each new autoconfirmed accounts; overrides 'user'
(although that should probably be 'non-autoconfirmed'…).
Upstream bug:
https://phabricator.wikimedia.org/T169545
References:
https://lists.wikimedia.org/pipermail/mediawiki-announce/2018-September/000223.html
I'm not sure why I didn't file bugs against 3.9 and 3.10 earlier. I confirmed the latest tagged containers are still affected and am filing those trackers not.
(3.6 and 3.7 went EOL, so those are just being marked as such)