It sounds as though the controller may be stripping the domain from the
authentication sent to ACS (there may be other explanations for what is
occurring
1. Turn the logging level on the ACS to full
This is accomplished by going into system configuration, service
control, setting the logging level to full, then restarting services.
2. Run a test with the problematic Aruba controller
3. Run the same user in a test with one of the working controllers.
I hope it will help you for troubleshooting