I believe Logon is reverting to 1st domain.
I just noticed this in build 860, but it may appear in others.
If you use a domain on the URL, using the LogonOp.do option. Example: ......../logonOp.do?domain=testdomain
If you login the first time everything works fine. However, if you mistype something and you get the "Invalid credentials or access denied, please try again" error message the URL has now dropped the domain and you will then be attempting to login to a totally different domain.
I haven't checked the other logonGuest.do, logon.do .... but it is a problem with logon.Op.do and maybe the others.