Odd behaviour when username includes directory separator symbol

localhost is POP!OS, 21.10, derived from Ubuntu
Grav v1.7.25 - Admin v1.10.25

Steps to reproduce:
Create user where the user name includes the forward-slash character (/).
For example, user/name

Result:
Instead of getting a yaml file with the username as the filename, you get a directory named for the characters preceding the forward-slash that contains a yaml file with a name taken from the characters following the forward-slash.
For example: user/
name.yaml

Other effects:
That username does not show in the list of users on the accounts page, so cannot be modified or deleted at the admin interface. I had to go to the file system to delete the directory structure and file associated with the user.

Login in seems to work normally.

Tests not performed:
I did not test the full range of non-alphanumeric characters.
I did not test languages other than English.
I did not do a deep dive on login tests to see if there are any unexpected login effects.

Other observations:
I don't know if there is a reasonable use case, but if you wanted to hide usernames from the listing under Accounts for any reason, this would be one way to do it.