User / share acces in place for a user that left the group that he belongs and where the folder got shared to

I’m using NC12b2.

Here is a userstory that I would like to bring to your attention and where I’m struggling with.

I created a user1 and a user2.
user1 is a manager of a new team (group team1) and makes a directory called team1 and shares that out to user2
user1 and user 2 both add files to the directory and shared location as team1.

Now user1 takes on another mananagement position and leaves team1 (as a group).
Then it turns out that although he left group team1 he can still see all team1 files and folders including all new files added by users like user3 (a new user at team1 group).

How can I now handover ownership to user2 for all the rights on the team1 directory in such a way that user1 can no longer see the files in team1 folder ? At the moment this is not possible.

Please advise? Or did I missed a feature?