Are these deployments being used with existing user profiles, or are new user profiles being created each time? It could be something residual in an existing user profile.
Is the same logon used on all four machines? If not, can you try using the same logon and see if that changes anything.
You could also try extracting the registry files from the image using Ghost explorer, and mounting them on an existing machine to verify the default policy setting in the image.
Finally, is there anything in the event logs to give additional clues as to what might be going on?