special characters in user names etc

This is not a question, but a tip for a solution. I found out, that if I had a WP user having special characters in his name, I could not add him af a service provider. By that I mean ä (a umlaut), ø å and maybe others, i did not check them all out. I'd look for the coding of the DB table to check if something i freezing up things there.
I replaced the ä in the name, and everything works fine.