TeamForge uses local user accounts on the SCM server to provide access to CVS repositories via ssh.
If any local user accounts on the SCM server match user names within TeamForge they will be changed.
If you are planning to use CVS in the SCM server, you should ensure that the local accounts do not conflict with the TeamForge user accounts. Adding a prefix to the local user accounts (local_username) would be one way to resolve this and prevent the usernames from conflicting. Alternatively, if you are not using CVS repositories, the CVS integration can be removed altogether.