USERS LOGGING AS USERNAME.DOMAINNAME.COM

Sometimes,when somebody loggs in windows 2003 network,a folder is created C:\documents and settings\username.domainname.com,and it should be C:\documents and settings\username,without the suffix,so the documents of a user is not available,because it looks like as if itz is logging as username.domainname.com,instead of username.
Does any body knows why?