Email from name -field can't have special characters

It seems like field email_from_name can't include special characters (like ä, å, å, ü) or mail can't be send. Webform tries to convert sender name to UTF-8, but something fails and mail is not sent. Instead error is presented to the user (which is correct behavious in case of error).

Simple solution for this is not to use any special characters at this moment. Fix would be welcome, though.