We just recently upgraded from Moodle 2.6.x to 2.8.5 and noticed that this change adversely affects certain configurations.
For example, one course had a forum set up with separate groups composed of 1 person per group (so as to use the forum as an internal 1 on 1 support system, similar to email), and individuals from other groups were now able to see messages in others' forums. We noticed that when a grouping was selected previously with the option to limit access to that grouping only, replacing this option with the new conditional setting when upgrading to version 2.8.5 seemed to have broken the forum's initial setup.
I now have the teacher going through each forum to delete the conditional option and simply use separate groups with a grouping, which works fine for her needs.