Username with German or French letters gets encoded and passes validation ASP.NET Core Identity

On .Net Core 3.0 Preview 3, Asp.NET Core Identity Template, register a user with username
`bernhard@günter.com
`
**Expected**
Validation responds that this is not an allowed character for a username since the default is
`
public string AllowedUserNameCharacters { get; set; }
= "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-._@+";
`
**Result**
`bernhard@xn--gnter-kva.com
` is stored in the db as username and email and displayed in the UI!

That is pretty unexpected for an old framework and a handicap in the current implementation.
Probably this has been encountered in the past??