I ran into an oddity recently with my live site I am mentioning here, to see if we can replicate it.
The site is currently Joomla 3.4, Kunena 4.0, and CB2 / GJ3, all upgraded from prior versions (since Joomla 1.5... LONG time!).
One of our GJ groups was doing housekeeping, and demoting old members that haven't been around any more. In this case, the admin demoted and removed an old Moderator who hadn't been in the community in almost a year. When she did, she noted that the old Moderator was still listed as a Moderator on the Kunena forum / board, even though they were no longer a part of the group.
I have a backup of the site I can restore for testing if needed, but wanted to see if anyone else had run into this before going through that step.