Users have domain after username

[Tim Hunter]

When I look at the Users folder on my two terminal servers, most of my users just show their username. For example: aroberts, chunt, cpowers, etc. It shows first initial and last name. Then I have a few users that show their username plus our domain name. For example, chendricks.wynnetr, administrator.wynnetr. What causes the domain to show on some of the users? Is there a way to fix this? Thank you.

[#2]

The users have logged on both locally and to domain.

If you logon to the local machine first, then to the domain you would end up with two profiles.
%username%
and
%username%.%userdomain%
Else if you logon to the domain first, then to the local machine you would end up with
%username%
and
%username%.%computername%