Shared files and folders permissions

Hello, Folks!
I am testing NextCloud and stepped into an issue, which i’ll be happy to get helped or advised about.

Overall picture is as follows:
NC installed on Ubuntu 16.04. I have an ldaps been set up and working as expected.
Authentication and sharing are based on Active Directory groups and also work fine.

However i want 1 account (NextCloud built-in admin) to be able to manage all NC resources.
So i decided to create all folders under admin account and then share them to appropriate groups.
However only the admin must have the right to delete files and folders (All others can create / edit / create folders etc).

And now is the thing:
I logged in with admin account, created a folder, shared it and un-ticked the “can delete”.
Now everything that is created in this folder can not be deleted by anybody, including the admin himself.
The only way is to delete the shared (root) folder.

Can you please advise/guide me how this can be solved?

i just tried to reproduce this with no success.
there is just one way i could imagine such a behavior: is the admin in the group you shared the file with?

Nope, The group is an Active Directory group and the admin is the NC out-of-the-box account