There are a lot of other users of User Role Editor which think different – they need multiple roles assignment to one user at WordPress. Historically, I developed this feature after I got multiple requests about it from plugins users.
I will add a user interface for this option (swith ON/OFF other roles section) later.
Currently it’s possible to manage this feature via filters, if your setup it correctly. This is a short demo video.
Check if you don’t have any accident typos in a code and it’s really executed. For example, code above works for the user with ‘user-manager’ role only. Did you change a role ID for your own or may be remove role checking code?