By default OpenAM will not enforce session quotas when running in Site mode without session failover (known as multi server mode in the code). This default behaviour is currently not covered in the OpenAM documentation.
A new option to enable enforcing session quotas using local session counts has been added as part of this sub-tasks parent task. The option can be added using the Advanced section of the Servers and Sites configuration and is enabled by setting openam.session.useLocalSessionsInMultiServerMode to true. This will mean that when in Site mode without session failover, per-instance session quotas can be enforced.