Remaining connections after removing OG Subgroups fields

It's a very strange issue and I'm not totally sure it is because of only OG Subgroups other components of my site would be affected too.
I had originally 2 content types: Exam is the group, Thesis is the group content. Then I added Administration content type which is a group and made Exam be group content. So the final structure is:
- Administration (group)
-- Exam (group and group content)
--- Thesis (group content)
I added Group user inheritance and Group permission inheritance fields to Exam content type and it seemed to work perfectly because I saw the 'Inherited users' block and after I connected an Exam node to an Administration node I saw the list of inherited users below the users of that Exam group.
But the inheritance of permissions didn't worked (I'd like to create a global editor role in an OG- and Workflow-based site, as I described in this issue), so I wanted to create a different setup. Therefore I deleted all additional OG-fields from each affected content type in 'OG field settings' page and here comes the strange part: After I removed the connection from between the Administration and Exam content types, the list of inherited users from the related Administration node has been still there in the 'People in group xxxx-exam-node' page.
I tried in many ways to get rid of it: disabled, removed and enabled the OG Subgroups module, clear the cache, clear the cache with drush, emptied cache tables in DB, rebuilt access rights etc. I also tried to find in the database where these connections are stored - without any success.

So I'd like to know what might cause this issue and how can I completely remove the OG Subgroups settings?