Following on from a report that was able to be reproduced by @simon, it’s been found that groups are visible even when they should not be to users who are a member of a specific group.
From my perspective, this is happening:
Let’s say that I am in Group 1 and Group 2, and being in these groups gives me access to Category 1. However, when I click the link to share the link from Category 1, the warning says that it can only be viewable by people in Group 1, Group 2 and Group 3. However, not being in Group 3, the group name should not be visible to me whatsoever.
There’s probably a better way of explaining this, though I think it’s best I leave it to someone with more technical knowledge about this issue.