It seems that this has been fixed in Xenial or at least I don't see this in logwatch at Thu, 21 Jan 2016 15:04:42 +0200 (EET).
** Changed in: logwatch (Ubuntu) Status: New => Fix Released -- You received this bug notification because you are a member of Ubuntu Server Team, which is subscribed to logwatch in Ubuntu. https://bugs.launchpad.net/bugs/1532252 Title: Unescaped left brace in regex is deprecated To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/logwatch/+bug/1532252/+subscriptions -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs