Yes it is coming from first versions of SambaPOS. We’re using # char for special cases and that can’t be used inside rule parameters. I’ve didn’t changed it for backwards compatibility but I can implement something to escape that in next versions.
Since that change will update database to replace # chars I’ll recommend creating a database backup before upgrading for a case of a required version downgrade. That will happen automatically for Backup Module users if Auto Backup on Migrate setting is enabled (enabled by default).