It's more to do with the actual permission.
Never >> Yes >> No.
Any group you're in with a never permission will stop you doing that thing, regardless of any other permissions. In your instance, one of the groups has a never permission for the ability to post without approval.
If you were in several groups with a no permissions to, say, make a new topic, and one group was set to yes, the yes permission will override all of the no's meaning you can post.