Well that's what i thought too if the chaining methods are swapped around a bit. My licensing work around solution was something along the lines of:
1. All Alfresco AD users are put into a group
2. This group is synced into Alfresco on a daily basis.
3. The chaining is changed to Alfresco, LDAP1 (our AD), LDAP2 (other AD)
This means that when a user tries to logon their account details are first checked against the MySQL data held in Alfresco if this is a match the user is logged in. Else it tries to match with details on our AD server, then tries another AD server and if all these fail then the user cannot login.
And as the alfresco server is talking to the AD server this would only need one CAL i think.
Thanks, Ben