Docker version of Roundcube not logging anything (no debug output)

[robod]

I have the latest docker image and I'm having trouble sending emails via SMTP. Trying to figure out what I've done wrong. I don't see anything obvious as the settings are the same as in Thudnderbird. So I've tried to enable smtp_debug and other logging. However, whatever I do, I can't get any logs out of it.

In /var/roundcube/config/config-extra.ini.php I've added:
$config['imap_debug'] = true;
$config['smtp_debug'] = true;

Not a beep.
So looking at defaults.ini.php, I've added to make sure it's going to the right place:
$config['log_dir'] = '/var/www/html/logs/';
$config['log_driver'] = 'file';

Making sure /var/www/htmo/logs has the right permissions and owner/group.
Again not a beep.
Nothing on console.

Am I doing anything wrong or has this been disabled/changed in the docker version?