Cannot set SMTP password in E-Mail Server settings

If I set up the SMTP configuration in the base settings, the password is not stored. All other settings can be found in the config.php, the password is not updated. So the email test fails. When I edit the config.php and set the mail_smtppassword variable there, it is working. Is this a bug that should be reported?

Nextcloud version: 15.0
Operating system and version: Debian 9.6
Apache or nginx version: Apache 2.4.25
PHP version: 7.2

The issue you are facing:

Is this the first time you’ve seen this error? (Y/N): Y

See above

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

  'mail_from_address' => 'nextcloud',
  'mail_smtpmode' => 'smtp',
  'mail_sendmailmode' => 'smtp',
  'mail_domain' => '',
  'mail_smtphost' => '',
  'mail_smtpport' => '587',
  'mail_smtpsecure' => 'tls',
  'mail_smtpauth' => 1,
  'mail_smtpauthtype' => 'LOGIN',
  'mail_smtpname' => 'my login name',
  'mail_smtppassword' => 'xxxxxxxxxxx',