Smart groups that are based upon advanced search => membership are broken after upgrade from 4.6.4 to 4.6.5. After the upgrade, the groups have everyone in the database and is not limited to the membership previously selected.
When you select contacts in group and then click on the edit smart group search criteria you get the advanced search form. The section for membership is expanded but the group is not selected nor is membership status filled in.
You can manually fix it and then it works, but having to go into every smart group one has and see if it's broken and then manually redo after you upgrade seems a bit much