Joomla not logging PHP errors to file with system default error_reporting

I’m using Joomla 3.9 with APACHE + PHP 7.0 with these settings

php_flag[display_errors] = On
php_flag[display_startup_errors] = On
php_value[error_reporting] = E_ALL & ~E_DEPRECATED & ~E_STRICT & ~E_NOTICE
php_flag[html_errors] = On
php_admin_flag[ignore_repeated_errors] = Off
php_flag[log_errors] = On
php_admin_flag[log_errors] = On
php_value[log_errors_max_len] = 1024

When Joomla error_reporting is set to development, errors are shown on the site and also logged in the error log file. When error_reporting is set to default it should still do the same since according to the documentation"

“System Default” leaves the level of PHP error reporting to that set up in the server (usually in the php.ini file).

However nothing is shown OR logged. If I create a test.php on the root of site (so that it bypasses the Joomla core) with an error — that error is logged so the PHP settings are working correctly.

Is Joomla doing something else or could this be a bug?