Users in one group can see people in other groups

[ixmann99]

Steps to reproduce

1. Activate "Restrict users to only share with users in their groups".
2. Create a user user1 in group1.
3. Create a user user2 in group2.
4. User "user1" in group1 can now click contacts and see "user2"! No further action is possible, but it is bad enough.

Expected behaviour

Should not show users from other groups. Often, you want group-isolation and this effectivly removes the option.

Actual behaviour

Shows all users, from all groups...

Also confirmed by multiple users in the forum. No errors in log.

Server configuration

cPanel / Centos 7

Operating system:

Web server:

Database:
MariDB

PHP version:
5.4, 7.0, 7.1

Nextcloud version: (see Nextcloud admin page)
12.0.0.

Updated from an older Nextcloud/ownCloud or fresh install:
No.

Where did you install Nextcloud from:
cPanel.

[rotanid]

really bad thing, but this is a duplicate of #5107 (and #5333 is also a duplicate)