Currently, in Manage Groups >> Settings (civicrm/group?reset=1&action=update&id=x) you can assign a group type of "Access Control" to Smart Groups. However, we don't actually allow Access Control Roles to be assigned to Smart Groups (i.e. they cannot be used as Access Control groups) - and we dont' support this functionality.
In order to prevent confusion, we need to modify the Groups >> Settings form to disable the "Access Control" checkbox for Smart Groups.
Also, add a statement in the 1.9 to 2.0 upgrade script which removes the "Access Control" group_type from an Smart Groups.