Steps to reproduce

1. share something with an email address to create a guest user guest@example.com
2. as an admin, on the user management page, select user guest@example.com to be the subadmin of some group
3. login as user guest@example.com and navigate to user management page

Expected behaviour

I don't know - should guest users be able to be made a subadmin of a group?

Actual behaviour

The guest user can change passwords of users in the group, delete users in the group etc.

Server configuration

Current core master.