Never connected Linux machines to a AD before so dont have a lot experience in that area but sounds to me like when you try to log on to your local accounts it tries to verify them against the AD.
Have you set your default domain to the domain you're trying to log into or do you have to type domain\username (think it's actually domain\\username when you do it from Linux but could be mistaken).
Not sure how it works on Linux against the AD and if you've set the default domain but on Windows machines you usually have to enter computer-name\local_username to log in locally.
Found a link that might be of assistance to you as well http://www.mail-archive.com/likewise.../msg00522.html
Hope it helps somewhat at least to figure out what might be causing the login problems for you.